Random encounter

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How it works
Implementations
Variants and combinations
History
Related
Games
References
Sources

A random encounter is a battle that a random roll starts while the player moves through the world. The Gameplay Design Patterns wiki describes random encounters as “created randomly usually from a predefined set of characteristics”, archetypically a fight with wandering monsters¹. The five games in the table roll once per step to decide whether a fight starts^2,3,4,5,6. Final Fantasy and the Pokémon games then roll again to pick the opponents^7,8,9,10.

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By terrainDragon Warrior (1986). Fights come most often on sand and hills and least on open ground.^2,11,12,13Dragon Warrior II (1987). Fights come most often in the mountains and least at sea.¹⁴
By areaFinal Fantasy (1987). Fights come at random as the party walks, rarely at sea, at a rate each dungeon sets.^3,7EarthBound Beginnings (1989). 32 to 5 in 256 per step by area, falling for a while after each fight.¹⁵Final Fantasy III (1990). How often battles come depends on the world the party is in and how it travels.¹⁶Final Fantasy IV (1991). How often battles come depends on the region of the world map.¹⁷Pokémon Red and Blue (1996). Each step in grass or water rolls against the map's rate in 256, then picks one of 10 slots.^4,8,18Pokémon Yellow (1998). Red and Blue's per-step roll, now reading a different tile so Cinnabar's coast gives no grass encounters.¹⁹Pokémon Ruby and Sapphire (2002). 16 times the area's rate out of 2,880 per step, with bike, flute, Cleanse Tag, Stench, and Illuminate modifiers.²⁰Pokémon Emerald (2004). 16 times the area's rate out of 2,880 per step, with bike, flute, item, and ability modifiers.^6,21,10,22Pokémon FireRed and LeafGreen (2004). A step cooldown, then a roll out of 1,600 on its own generator that grows easier with each failed check.^23,24Pokémon HeartGold and SoulSilver (2009). A gate set by movement, very tall grass, the radio, and turning in place, then the map's one rate; 12 slots whose species change with the time of day.^25,26,27,28
By area and timePokémon Gold and Silver (1999). The map's rate and its grass slots for morning, day, or night, then one of 7 slots.^29,30Pokémon Crystal (2000). The map's rate for morning, day, or night, then one of 7 grass slots.^5,9
Area times terrainDragon Warrior III (1988). Fights come more often in harsher places, and on the world map more often at night.^31,32
Danger counterFinal Fantasy V (1992). Every step makes a battle likelier until one comes.³³Final Fantasy VI (1994). Final Fantasy V's counter at half the normal rate, $70 per step.^34,35,36

#How it works

on each step onto a tile that allows fights:
    if a cooldown is running: count it down; no fight        # the Pokémon games
    if roll() < rate(map, terrain, modifiers):
        opponents = weighted_pick(area_table)               # slots or formations
        start the battle

With a chance $p$ per step and no cooldown, the wait for the next fight is geometric and averages $1 / p$ steps.

	Chance per step	Changed by	Opponents	Grace after a fight
Dragon Warrior	1/8 · 1/16 · 1/32 or 1/16^2,2	terrain and position; halved or quartered near Tantegel¹¹	—	—
Final Fantasy	10 in 256 per step (3 at sea)³ on the overworld; a per-map rate elsewhere³	the ship³	8 formations, 12 · 12 · 12 · 12 · 6 · 6 · 3 · 1 (of 64)^7,7	—
Red and Blue	the map’s rate in 256, 25 on Route 1⁴	grass or water⁴	10 slots, 51 · 51 · 39 · 25 · 25 · 25 · 13 · 13 · 11 · 3 (of 256)^8,8	a counter of 3 steps¹⁸
Crystal	the map’s rate for the time of day, 25 in 256 on Route 29⁵	radio music, Cleanse Tag⁵	7 slots, 30 · 30 · 20 · 10 · 5 · 4 · 1 %^9,9	—
Emerald	16 × rate in 2,880 per step^6,6	bikes, flutes, Cleanse Tag, lead ability; a change of tile type^6,21	12 slots, 20 · 20 · 10 · 10 · 10 · 10 · 5 · 5 · 4 · 4 · 1 · 1 %^10,10	4 checks²²

#Implementations

#Dragon Warrior

Each step on the map draws a byte and starts a fight when the bits the terrain selects are all 0². Hills and sand use 3 bits, 1 in 8; swamp, forest, brick, and barrier squares use 4, 1 in 16². Other ground uses 5 bits where the X and Y coordinates are both even or both odd, and 4 elsewhere, so open plains alternate between 1 in 32 and 1 in 16². Around Tantegel Castle a second byte lets only half of those fights through, and a quarter on hills¹¹.

The NES manual tells a different story. It says monsters come out to attack and that “If you happen to bump into one of them, the game will automatically enter the fight mode”¹². The map holds no monsters to bump into; the per-step roll starts every fight². The manual’s terrain guide does match the code’s order: fewer monsters on plains, more in forests, and “many enemies” in the hills it calls mountains^13,2.

#Dragon Warrior II and III

The North American Dragon Warrior II gives each terrain one rate, 4/255 (sea) to 25/255 (mountains) per step¹⁴, against a random byte from 1 to 255, where Dragon Warrior tests the bits the terrain selects^14,2. Below map $2B, only the world map and Moonbrooke have encounters¹⁴. The North American Dragon Warrior III multiplies the terrain’s odds by a factor from the area’s encounter class, for up to 100/256 per step; higher at night^31,31. Carrying the Golden Claw sets the odds to 100³¹.

#Final Fantasy

On the overworld, a step onto a tile marked for fights starts a battle when the battle-step generator returns less than 10, or less than 3 aboard the ship³. In dungeons and towns the threshold comes from a table with one rate per map³. A second counter then indexes the same 256-byte table to pick one of the area’s 8 formations, weighted 12 · 12 · 12 · 12 · 6 · 6 · 3 · 1 (of 64)^7,7.

That table holds every byte once, and the step generator walks it one entry per call^37,38. The overworld rate therefore holds exactly over each pass of 256 draws, as well as on average. The formation weights are exact in the same way over 256 battles⁷.

#Final Fantasy III to VI

Final Fantasy III loads a world-map rate for each world and vehicle, 5 in 256 per step (7 underwater)^16,16. Those rates come from the listing’s comments, because the data bytes aren’t in the listing and no Japanese ROM is on hand to read them¹⁶. Final Fantasy IV reads its overworld rate, 7–10 in 256 per step¹⁷, from an 8 × 8 grid of map regions, against a byte from a fixed random table plus an offset that grows each time the step counter wraps¹⁷.

Final Fantasy V adds the map’s rate to a counter on each step, $E0 at the normal rate, and starts a battle when a random byte is under the counter’s high byte³³. Final Fantasy VI keeps that counter and halves the normal rate to $70 per step^35,33. A battle clears the counter, so each step without one makes the next likelier³⁴. On Final Fantasy VI’s world map, a bug the disassembly marks keeps the battle rate and group of an old position until a battle, an event, an entrance, or the world map’s start updates them³⁶.

#Pokémon Red and Blue

On each step in grass or water, TryDoWildEncounter starts a battle when the byte hRandomAdd is below the map’s rate⁴. Route 1’s grass rate is 25, so a step in its grass starts a battle 25 times in 256⁴. The byte hRandomSub, from the same generator step, then picks one of the map’s 10 slots with chances 51 · 51 · 39 · 25 · 25 · 25 · 13 · 13 · 11 · 3 (of 256)^8,8. After a battle, a counter of 3 steps holds off the next wild battle¹⁸.

Pokémon Yellow’s TryDoWildEncounter tests the bottom-left tile of the player’s half-block where Red and Blue test the bottom-right, so “left shore” half-blocks such as Cinnabar Island’s east coast no longer load grass encounters¹⁹.

#Pokémon Crystal

Crystal gives each grass area three rates, for morning, day, and night, and uses a separate water rate⁵. The Pokémon March and the Ruins of Alph radio double the rate; the Pokémon Lullaby and a Cleanse Tag in the party halve it⁵. A second roll from 1 to 100 picks one of 7 grass slots⁹.

Pokémon Gold and Silver already have these rates, modifiers, and slots, which Crystal keeps unchanged^29,30.

#Pokémon Emerald

Emerald multiplies each area’s rate by 16 and compares it with Random() % 2880, after modifiers for the Mach and Acro Bikes, flutes, a Cleanse Tag, and the lead Pokémon’s ability⁶. Route 101’s rate of 20 gives 320 in 2,880, 1 in 9⁶. A step onto a tile whose behavior differs from the last one skips the check 40% of the time²¹. After a battle starts, and whenever a map loads, the next 4 checks are skipped²².

Pokémon Ruby and Sapphire use the same roll out of 2,880, with bike, flute, Cleanse Tag, Stench, and Illuminate modifiers; Emerald adds more ability modifiers^20,6. Pokémon FireRed and LeafGreen roll on a generator of their own, and a check passes when its value mod 1,600 is below 16 times the area’s rate plus part of a buff that every failed check raises²³. Before that roll, they require a minimum number of steps since the last battle, letting a check through earlier only on a 5-in-100 roll²⁴.

#EarthBound Beginnings

In the English build of EarthBound Beginnings, each step in an area with encounters starts a fight at 32/256 to 5/256 per step¹⁵, set by the area’s frequency class plus a counter¹⁵. Each encounter raises the counter, so the rate drops after fights until the player enters an area without encounters or passes a fade-out¹⁵. Red and Blue instead hold off the next battle with a counter of 3 steps¹⁸.

#Variants and combinations

Fleeing is the usual exit from a fight the player didn’t choose. Dragon Warrior tests it with Agility, and the Pokémon games with Speed^39,40.
Random number generators decide how a rate plays out. Red and Blue read the generator’s two bytes, Final Fantasy walks a permuted table, and Emerald calls an LCG^4,38,41.

#History

The games read here run from Dragon Quest (Famicom, 1986) to Emerald (2004)^42,43. The Gameplay Design Patterns wiki names early editions of Dungeons & Dragons among the games with random encounters¹.

Games

Game	Year	How	Note
Dragon Warrior	1986	By terrain	fights come most often on sand and hills and least on open ground
Dragon Warrior II	1987	By terrain	fights come most often in the mountains and least at sea
Final Fantasy	1987	By area	fights come at random as the party walks, rarely at sea, at a rate each dungeon sets
EarthBound Beginnings	1989	By area	32 to 5 in 256 per step by area, falling for a while after each fight
Final Fantasy III	1990	By area	how often battles come depends on the world the party is in and how it travels
Final Fantasy IV	1991	By area	how often battles come depends on the region of the world map
Pokémon Red and Blue	1996	By area	each step in grass or water rolls against the map's rate in 256, then picks one of 10 slots
Pokémon Yellow	1998	By area	Red and Blue's per-step roll, now reading a different tile so Cinnabar's coast gives no grass encounters
Pokémon Ruby and Sapphire	2002	By area	16 times the area's rate out of 2,880 per step, with bike, flute, Cleanse Tag, Stench, and Illuminate modifiers
Pokémon Emerald	2004	By area	16 times the area's rate out of 2,880 per step, with bike, flute, item, and ability modifiers
Pokémon FireRed and LeafGreen	2004	By area	a step cooldown, then a roll out of 1,600 on its own generator that grows easier with each failed check
Pokémon HeartGold and SoulSilver	2009	By area	a gate set by movement, very tall grass, the radio, and turning in place, then the map's one rate; 12 slots whose species change with the time of day
Pokémon Gold and Silver	1999	By area and time	the map's rate and its grass slots for morning, day, or night, then one of 7 slots
Pokémon Crystal	2000	By area and time	the map's rate for morning, day, or night, then one of 7 grass slots
Dragon Warrior III	1988	Area times terrain	fights come more often in harsher places, and on the world map more often at night
Final Fantasy V	1992	Danger counter	every step makes a battle likelier until one comes
Final Fantasy VI	1994	Danger counter	Final Fantasy V's counter at half the normal rate, $70 per step

Every claim about this mechanic, by game (43)

Dragon Warrior 1986	Each step on the map draws a byte and starts a fight when its masked bits are all 0: 1 in 8 on sand and hills, 1 in 16 in swamp, forest, brick, and barrier squares, and on other terrain 1 in 32 where the X and Y coordinates are both even or both odd, 1 in 16 elsewhere.	Code
	On the overworld's zone 0, the slime-only region around Tantegel Castle, a second byte lets only half of those fights through, and a quarter on hills.	Code
	The NES manual describes encounters as meeting a monster on the map: "If you happen to bump into one of them, the game will automatically enter the fight mode."	Manual
	The NES manual's terrain guide says fewer monsters live on plains, more lurk in forests, and mountains bring "many enemies".	Manual
	Each fight picks one of its zone's five monster slots with equal chance; zone 0, around Tantegel Castle, holds three Slime slots and two Red Slime slots, and zone 1 adds a Drakee, all with dodge 1.	Code
	The Demon Knight, the hardest monster to hit at 15/64, fills one of the five slots in overworld zones 10, 11, and 12; the Werewolf, at 7/64, fills one in zone 12 and in zone 13, which Hauksness also uses, and one on the Dragonlord's castle ground floor.	Code
	The Dragonlord's castle's six sublevels draw from three rows, Werewolf, Green Dragon, Starwyvern, Wizard, and Axe Knight on the first; Wizard, Axe Knight, two Blue Dragons, and Stoneman on the next three; and Wizard, Stoneman, two Armored Knights, and Red Dragon on the last two and the bottom floor. Apart from the Werewolf's 7, their dodge nibbles are 1 or 2.	Code
Dragon Warrior II 1987	In Dragon Warrior II (the North American NES release), each step draws a random byte from 1 to 255 and starts a fight when the terrain's rate is at least that byte: on the world map 10 on grass, 16 in forest, desert, and swamp, 25 on mountains, and 4 at sea; 8 on maps numbered $2B and up and in Moonbrooke, while the other maps below $2B have none.	Code
Final Fantasy 1987	On the overworld, a step onto a tile marked for fights starts a battle when the battle-step generator returns less than 10, or less than 3 aboard the ship; in dungeons and towns the threshold is a per-map rate.	Code
	`GetBattleFormation` picks one of the area's 8 formations by indexing `lut_RNG` with a counter that rises by 1 per battle; the low 6 bits select formations 0–3 with 12 chances in 64 each, 4 and 5 with 6, 6 with 3, and 7 with 1.	Code
	A new game puts the party at overworld tile (153, 165), in land domain $2C, whose eight formation slots all hold 3–5 Imps (evade 6). The domain to its north, $24, gives 3–5 Imps in 48 of 64 battles; its other slots hold 1–3 GrImps (evade 9), 1–2 Wolves (36), a lone Madpony (22), and, 1 time in 64, 3–6 Imps with up to 4 GrImps.	Code
	The Air elemental (evade 144) is in the random battles of five standard maps, $2F, $30, $32, $33, and $3A, as 2–4 or 3–6 of them in one 12-in-64 slot of the last three, to which $32 and $33 add a second, smaller slot of 1–3 (15 and 18 of 64 in all); Wraith (108) fills 42 of 64 chances on map $25, Frost D (120) 30 of 64 on map $34, and Sphinx (120) 24 of 64 on map $0E and 12 of 64 in four overworld domains.	Code
	Nintendo Power's guide places Wraiths in the Ice Cave and Air elementals in the Sky Castle.	Magazine
Dragon Warrior III 1988	In Dragon Warrior III (the North American NES release), each step reads the area's encounter class: classes 0–2 first pass a roll of 16, 64, or 128 in 256 and then use a multiplier of 1, and classes 3–7 use 1, 2, 4, 8, or 16. The multiplier times the terrain's odds, capped at 100, is then compared with a random byte; the overworld's odds rise at night (grass 10 by day and 13 by night, forest 18 and 22, hills 25 and 31, and 4 and 5 aboard the ship, which uses terrain 0), and carrying the Golden Claw sets them to 100.	Code
EarthBound Beginnings 1989	In EarthBound Beginnings (English build), each step in an area with encounters starts a fight when a random byte is below a rate from the table 32, 21, 16, 13, 10, 8, 6, 5 (in 256), indexed by the area's frequency class (1–7) plus a counter, capped at the eighth entry. The counter rises by 1 with each encounter, up to 2, so the rate drops after fights; it returns to 0 in areas without encounters and after a fade-out transition.	Code
Final Fantasy III 1990	On the world map, a step starts a battle when a random byte is under the rate loaded for the current world and vehicle; the listing's comments give those rates as 5 on foot, by canoe, or by ship, 7 underwater, and 18 for one chocobo case the disassembly marks with "???".	Code
Final Fantasy IV 1991	On the overworld, each step reads a rate from an 8 × 8 grid of map regions (7, 8, or 10) and starts a battle when a byte from a fixed random table, plus an offset that grows by $11 each time the step counter wraps, is below it.	Code
Final Fantasy V 1992	Each step on a normal map adds the map's rate to a random-battle counter ($E0 at the normal rate; $40, $180, or $200 at the others), and a battle starts when a byte from the random table, plus an offset that grows by $11 each time its pointer wraps, is under the counter's high byte.	Code
Final Fantasy VI 1994	Each step on a town or dungeon map adds the map's rate to a random-battle counter ($70 per step at the normal rate; $40, $160, or $200 at the low, high, and very high ones; the Charm Bangle halves them and the Moogle Charm zeroes them), and a battle starts when a byte from the random table, plus an offset that grows by 17 each time its pointer wraps, is under the counter's high byte. A battle clears the counter, so each step without one makes the next likelier.	Code
	On the world map, the sector that picks the battle rate and group is read from $1F60 and $1F61. While the player walks, the world map's movement code copies the current position there only in the branch taken after a random battle starts, so the rate and group stay as they were until a battle or another writer (world map start, events, entrances) updates them; the disassembly marks this as a bug.	Code
	Final Fantasy VI keeps Final Fantasy V's random-battle counter, which each step raises by the map's rate and which a byte from the random table, offset each time its pointer wraps, is tested against; it halves the normal rate from $E0 to $70 per step and changes the high one from $180 to $160.	Code
Pokémon Red and Blue 1996	On each step in grass or water, `TryDoWildEncounter` starts a wild battle when the byte `hRandomAdd` is below the map's encounter rate, out of 256; Route 1's grass rate is 25.	Code
	The byte `hRandomSub` then picks one of the map's 10 slots, which have 51, 51, 39, 25, 25, 25, 13, 13, 11, and 3 chances in 256.	Code
	After a battle, `EnterMap` sets a counter of 3 that each step decrements, and no wild battle can start while it is above 0.	Code
	Pidgey learns Sand-Attack at level 5, and a wild or trainer Pokémon knows the moves its learnset gives up to its level; so Route 1's level-5 Pidgey (slot 9, 3 in 256 encounters), Route 2's (slot 4, 25 in 256), and the rival's level-9 Pidgey on Route 22 can use it.	Code
Pokémon Yellow 1998	Yellow's `TryDoWildEncounter` tests the bottom-left tile of the player's half-block where Red and Blue test the bottom-right, so “left shore” half-blocks, such as Cinnabar Island's east coast, no longer load grass encounters; the rest of the routine is unchanged.	Code
Pokémon Gold and Silver 1999	On each step, Gold and Silver's `TryWildEncounter` reads the map's encounter rate for the current time of day (morning, day, or night), or its water rate, doubles it for the Pokémon March or Ruins of Alph radio, halves it for the Pokémon Lullaby or a Cleanse Tag, and starts a battle when `Random` is below it; Crystal keeps this unchanged.	Code
Pokémon Gold and Silver 1999	The time of day picks which of a grass area's three sets of 7 slots is used; a roll from 1 to 100 then picks a slot at 30, 30, 20, 10, 5, 4, and 1 percent, or one of 3 water slots at 60, 30, and 10 percent. Crystal's routine and table are the same.	Code
Pokémon Crystal 2000	On each step, `TryWildEncounter` starts a battle when `Random` is below the map's rate for the time of day (morning, day, or night) or its water rate; the Pokémon March or Ruins of Alph radio doubles the rate, and the Pokémon Lullaby or a Cleanse Tag in the party halves it.	Code
Pokémon Crystal 2000	A second `Random` from 1 to 100 picks one of a grass area's 7 slots, at 30, 30, 20, 10, 5, 4, and 1 percent, or one of 3 water slots at 60, 30, and 10 percent.	Code
Pokémon Ruby and Sapphire 2002	Ruby and Sapphire multiply the area's encounter rate by 16, cut it to 80% on the Mach or Acro Bike, apply the flute and Cleanse Tag modifiers, halve it for a lead with Stench and double it for Illuminate, cap it at 2,880, and start a battle when `Random() % 2880` is below it. Emerald keeps the roll and adds more ability modifiers.	Code
Pokémon Emerald 2004	On each step onto grass or water, `WildEncounterCheck` multiplies the area's rate by 16, applies bike, flute, Cleanse Tag, and lead-ability modifiers, and starts a battle when `Random() % 2880` is below it; Route 101's rate is 20.	Code
	A step onto a tile whose behavior differs from the last one skips the encounter check 40% of the time.	Code
	Emerald's 12 land slots come up 20, 20, 10, 10, 10, 10, 5, 5, 4, 4, 1, and 1 percent of the time.	Code
	After a battle starts, and whenever a map loads, the next 4 encounter checks are skipped.	Code
Pokémon FireRed and LeafGreen 2004	FireRed and LeafGreen roll encounters on their own generator, $x \leftarrow 1103515245 x + 12345$ , seeded at a new game; a check passes when its value mod 1,600 is below 16 times the area's rate, cut to 80% on a bike, plus 16/200 of a buff to which every failed check adds the area's rate, reset by a battle or a Repel.	Code
Pokémon FireRed and LeafGreen 2004	Before that roll, FireRed and LeafGreen require a minimum number of steps since the last battle, 8 − ⌊rate/10⌋ (0 at a rate of 80 or more, 8 below 10), and before then let a check through only on a 5-in-100 roll; the flutes, a Cleanse Tag, and the lead's Stench or Illuminate scale both numbers.	Code
Pokémon HeartGold and SoulSilver 2009	HeartGold and SoulSilver fold the five periods into three for wild Pokémon (`GF_RTC_GetTimeOfDayWildParamByHour`: morning; day or evening; night or late night), and grass encounters pick their species list the same way. `IsNighttime` is true at night or late night, so from 20:00 to 3:59 (computed from the hour table), and the evolution methods tied to the clock read it: friendship of at least 220 by day (`EVO_FRIENDSHIP_DAY`) or by night (`EVO_FRIENDSHIP_NIGHT`), and a held item by day or by night (`EVO_ITEM_DAY`, `EVO_ITEM_NIGHT`).	Code
	When a step ends on grass or water, HeartGold and SoulSilver roll twice, each `LCRandom() % 100`. The first roll must fall below a gate that starts at 40, loses 20 unless the player is cycling or surfing or an unnamed avatar check (`sub_0205DE98`, still assembly) passes, gains 40 in very tall grass or else 30 when cycling, gains 30, 40, or 60 once a counter of reversed facings (`reverseTurnFrameSteps`) reaches 2, 3, or 4, and gains or loses 25 for the Pokémon March or the Pokémon Lullaby on the radio, capped at 100. The second must fall below the map's own rate for that terrain, capped at 100. A check comes only once a step counter (`encounterInhibitSteps`), which a wild battle or a warp clears, is past 3. Platinum's gate is 40, plus 30 in very tall grass or when cycling, adjusted on special dates, with no walking penalty, facing counter, or radio. Before its gate, Platinum adds a grace roll: while its count of attempts is below $8 - \min (⌊ r / 10 ⌋, 8)$ for the rate $r$ it is passed (computed), each attempt adds 1 to the count and goes on only if `LCRNG_RandMod(100)` is below 5; a comment says this covers the first attempts after each map transition or wild battle. HeartGold and SoulSilver's check has no such roll; they skip the check outright while the step counter is 3 or less.	Code
	Before the two rolls, HeartGold and SoulSilver adjust the map's rate in this order: the lead Pokémon's ability (unless it is an Egg) doubles it for Arena Trap, No Guard, or Illuminate, halves it for White Smoke, Quick Feet, or Stench, or for Snow Cloak in snow, capped at 100; the Black Flute halves it and the White Flute raises it by half; and a Cleanse Tag or Pure Incense held by the lead Pokémon cuts it to 2/3. Gold and Silver instead double the rate for the Pokémon March or the Ruins of Alph radio and halve it for the Pokémon Lullaby or a Cleanse Tag.	Code
	HeartGold and SoulSilver have 12 grass slots and 5 surfing slots, picked by one `LCRandom() % 100` against bounds in `EncounterSlot_WildMonSlotRoll_Land` and `EncounterSlot_WildMonSlotRoll_Surfing`, so they come up 20, 20, 10, 10, 10, 10, 5, 5, 4, 4, 1, and 1 percent and 60, 30, 5, 4, and 1 percent (computed from the bounds). Platinum's `GetGroundEncounterSlot` and `GetWaterEncounterSlot` have the same bounds. Gold and Silver have 7 grass slots and 3 water slots, with cumulative bounds in `GrassMonProbTable` (30, 60, 80, 90, 95, 99, 100) and `WaterMonProbTable` (60, 90, 100), so 30, 30, 20, 10, 5, 4, and 1 percent and 60, 30, and 10 percent (computed from the differences).	Code
	A HeartGold or SoulSilver map's encounter record holds one walking rate and three full species lists for its 12 grass slots, morning, day, and night, sharing one list of levels. Gold and Silver keep a separate grass rate for each time of day and three sets of 7 slots. Platinum keeps one 12-slot list and swaps only slots 2 and 3 for their day or night species outside the morning.	Code
general	The Gameplay Design Patterns wiki describes random encounters as encounters "created randomly usually from a predefined set of characteristics", archetypically a fight with wandering monsters, and names early editions of Dungeons & Dragons as an example.	Wiki

References

^ a bThe Gameplay Design Patterns wiki describes random encounters as encounters "created randomly usually from a predefined set of characteristics", archetypically a fight with wandering monsters, and names early editions of Dungeons & Dragons as an example.WikiGameplay Design Patterns wiki, “Ephemeral Goals”
How we know
These encounters are, as the name suggests, created randomly usually from a predefined set of characteristics. The archetypical random encounter is to defeat a group of wandering monsters or enemies. … Many Tabletop and Computer-based Roleplaying Games use random encounters during the gameplay, e.g. early editions of Dungeons & Dragons and the Elder Scrolls series.
Examples · archived copy ↗
The quote matches our archived copy.
In the claim ledger

^ a b c d e f g h i jEach step on the map draws a byte and starts a fight when its masked bits are all 0: 1 in 8 on sand and hills, 1 in 16 in swamp, forest, brick, and barrier squares, and on other terrain 1 in 32 where the X and Y coordinates are both even or both odd, 1 in 16 elsewhere.Codenmikstas/dragon-warrior-disassembly

How we know

1888LCDA2:  JSR UpdateRandNum       ;($C55B)Get random number.

source_files/Bank03.asm lines 1887–1888 at ebe6a13 · upstream ↗

1949LCDFB:  LDA #$0F                ;Get random number.
⋮
1952LCDFD:  AND RandNumUB           ;Is lower nibble 0?
1953LCDFF:  BEQ DoRandomFight       ;If so, branch to start a random fight.
⋮
1957LCE02:  CMP #BLK_SAND           ;Is the player on a sand block?
⋮
1960LCE06:  CMP #BLK_HILL           ;Is the player on a hill block?
⋮
1968LCE13:  LDA #$07                ;Twice as likely to get into a fight in the sandy areas!
⋮
1972LCE17:  CMP #BLK_TREES          ;Is player on a tree block?     
⋮
1975LCE1B:  CMP #BLK_BRICK          ;Is player on a brick block?
⋮
1978LCE1F:  CMP #BLK_FFIELD         ;Is player on a force field block?

source_files/Bank03.asm lines 1948–1981 at ebe6a13 · upstream ↗

2025LCE63:  LDA CharXPos            ;Is character on an odd X map position?
⋮
2040LCE74:  LDA #$1F                ;Higher chance for fight. Check 5 bits instead of 4.

source_files/Bank03.asm lines 2020–2045 at ebe6a13 · upstream ↗

Checked against the evidence by its author, an AI model, 2026-10-20.

Checked by a second AI model, 2026-10-21.

#How it works

#Implementations

#Dragon Warrior

#Dragon Warrior II and III

#Final Fantasy

#Final Fantasy III to VI

#Pokémon Red and Blue

#Pokémon Crystal

#Pokémon Emerald

#EarthBound Beginnings

#Variants and combinations

#History

Related

Combines with

See also

Mentioned in

Games

References

Sources

Code

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