| HeartGold and SoulSilver (the US releases, which share this code) split the clock's hour into five periods with a 24-entry table: morning from 4:00 to 9:59, day from 10:00 to 16:59, evening from 17:00 to 19:59, night from 20:00 to 23:59, and late night from 0:00 to 3:59. Platinum's table gives every hour the same period (its names are morning, day, twilight, night, and late night). Gold and Silver have three periods: morning from 4:00, day from 10:00, and night from 18:00. | include/gf_rtc.h L8–15src/gf_rtc.c L164–193 | Code |
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). | src/gf_rtc.c L142–150src/gf_rtc.c L196–205src/field/encounter_check.c L119–130src/pokemon.c L2829–2839src/pokemon.c L2902–2909 | 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 for the rate 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. | src/field/encounter_check.c L565–590src/field/encounter_check.c L595–607src/field/encounter_check.c L623–627include/math_util.h L30–35src/field/encounter_check.c L1397–1428src/field/encounter_check.c L215–234src/field/encounter_check.c L315–318src/field_warp_tasks.c L268–269src/field/field_control.c L471–474src/field/encounter_check.c L1031–1039 | 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. | src/field/encounter_check.c L244–247src/field/encounter_check.c L1120–1140src/field/encounter_check.c L718–731 | 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). | src/field/encounter_check.c L632–676 | 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. | include/wild_encounter.h L23–28include/wild_encounter.h L36–44src/field/encounter_check.c L133–136 | Code |
HeartGold and SoulSilver's BattleSystem_CalculateBallShakes keeps Platinum's capture math: for catch rate , ball multiplier in tenths, max HP and current HP , ×2 for sleep or freeze and ×15/10 for burn, paralysis, poison, or bad poison, a catch at once when is 255 or more, and otherwise four 16-bit rolls each below , with the Master Ball's shakes set to four after the draw. The Ultra, Great, Poké, and Safari Balls keep Platinum's 20, 15, 10, and 15 (an assembly data table in the decompilation), and a Pal Park or tutorial battle always catches. | src/battle/battle_command.c L7145–7152src/battle/battle_command.c L7290–7327include/constants/battle.h L721asm/overlay_12_battle_command.s L17–18src/battle/battle_system.c L1112–1114 | Code |
In HeartGold and SoulSilver the Apricorn balls change the catch rate itself and leave the multiplier at 10, after which the rate is capped at 255 (a negative one becomes 1) and goes through the usual HP and status steps: the Fast Ball ×4 when the wild species' base Speed is 100 or more, the Level Ball ×2 when the attacking battler's (battlerIdAttacker) level is above the wild Pokémon's, ×4 when half its level (rounded down) is above it, and ×8 when a quarter of its level (rounded down) is, the Lure Ball ×3 when fishing, the Love Ball ×8 for the same species of the opposite gender, and the Moon Ball ×4 for the 14 species of the Nidoran, Clefairy, Jigglypuff, and Skitty families listed in an assembly data table. Crystal's Level Ball skips the HP and status steps, and its disassembly's comments mark the Moon Ball as never boosting, the Love Ball as boosting the same gender, and the Fast Ball as boosting only three species. | src/battle/battle_command.c L7218–7245src/battle/battle_command.c L7259–7288src/battle/battle_command.c L7161–7166asm/overlay_12_battle_command.s L132–146 | Code |
| HeartGold and SoulSilver's Heavy Ball adds 40 to the catch rate at 409.6 kg or more, 30 at 307.2 kg, and 20 at 204.8 kg, reading weight in tenths of a kilogram from the Pokédex data. Below 204.8 kg its last branch tests the catch rate against 1024 instead of the weight, and a catch rate is at most 255, so every lighter Pokémon loses 20 (a result below 0 becomes 1); a comment in the decompilation calls this a mistake. Crystal subtracts 20 only below 102.4 kg and adds nothing from there to 204.8 kg. | src/battle/battle_command.c L7246–7260src/battle/battle_command.c L7286–7288 | Code |
HeartGold and SoulSilver's TryCriticalHit keeps Platinum's critical-hit rule: the stage sum (+2 Focus Energy, +1 for a HOLD_EFFECT_CRITRATE_UP item, +1 Super Luck, +2 for Chansey or Farfetch'd with its own item, plus the move's boosts) capped at 4, a chance of 1 in 16, 8, 4, 3, or 2, blocked by Battle Armor or Shell Armor unless ignored, by Lucky Chant on the target's side, or by bit 15 of the target's move-effect flags (named MOVE_EFFECT_FLAG_LUCKY_CHANT here), and Sniper turning ×2 into ×3. | src/battle/overlay_12_0224E4FC.c L5960–5995include/constants/battle.h L177 | Code |