Final Fantasy Mystic Quest's battle rules (TheAnsarya's ffmq-info, Final Fantasy - Mystic Quest (USA) (Rev 1))

The game's random numbers come from one 16-bit state kept in save RAM at $70:1FFE: each call shifts it left twice, then adds the old state, $3711 and the frame counter at $0E96 in turn, each addition taking in the carry the step before left (the first takes bit 14 of the old state, which the second shift pushed out, so the step is 5 times the state plus that bit, not 5 times the state alone), keeps the 16-bit result, and returns its high byte, reduced modulo the range the caller puts in $A8 when that isn't 0. A range of $65 gives 0-100. ffmq/rng

About: Final Fantasy Mystic Quest Random number generator

Value: shifts 2 · increment 0x3711 · state $70:1FFE

The battle code calls it with $65 in $A8 for a draw of 0-100 (ffmq/formation-sets, ffmq/first-strike, ffmq/run). Because the frame counter feeds every step, the sequence depends on timing as well as the state.

The code at $00:A274 reads a word through the 24-bit pointer at $17 and moves the pointer past it, puts the word's low byte, the battle number, in $0513 and its high byte in $0A9C, and calls $00:D080 with the pointer saved. The battle setup at $02:8000 copies $0513 to $0514 unless it's $FF, and the number then picks the battle's formation set (ffmq-tables/formation-sets); battle numbers 0-19 are the battlefields. Not read here: the path from $00:D080 to the battle setup, and the dispatch that runs the code at $00:A274 as an event-script command. The manuals' account of battles on the map is ffmq/map-battles. ffmq/script-battle

By the US and Japanese manuals and Squaresoft's newsletter, monsters stand on the map in dungeons and towns, and walking into one starts a battle; the Overworld has no monsters to run into, and its battlefields are optional: 20 of them, each of 10 battles, with a prize for clearing one (ffmq-tables/battlefields). The code that stores a battle's number is ffmq/script-battle. ffmq/map-battles

About: Final Fantasy Mystic Quest Visible encounter

The battlefields are the US manual's Battlefield Icons and the Japanese manual's バトルポイント (battle points). The sources say contact starts a fight; none says in so many words that a monster can be walked around.

Cited by: Random encounter, Visible encounter

Before the first round the game rolls for a first strike. Unless the formation's flags byte has bit 7 set, it takes the monsters' figure as the first slot's level plus twice the second slot's plus 3 (an empty slot's level is $FF, so each slot counts its level plus one, and the third slot is never read), divided by the number of monsters, and the party's as Benjamin's level, averaged with the companion's when one is present; it draws 0-100 and, when the draw is at least 100 minus 10 times the difference (the difference capped at 10), gives the first strike to the side with the higher figure. Computed: a difference of d gives a first strike 10d + 1 times in 101. The party's first strike is a round in which only the party acts; the monsters' is a round in which only they act, and only in battle numbers 0-19, the battlefields. With bit 7 set the roll is skipped and the monsters strike first in a battlefield. ffmq/first-strike

About: Final Fantasy Mystic Quest Turn order

Value: cap difference 10 · per level 10

The monsters' slots are battle records $1100, $1180 and $1200, and a record's level is at offset $10, so $1110 and $1190 are the first two slots; the code adds the second twice where a sum over the three slots would read $1210. A party with no companion has $FF at $1090, which the code skips.

Cited by: Visible encounter

Each round the game gives every actor a key of its speed plus a random number below half its speed (0-255 when half its speed is 0), or 2 for an actor with status bit 6 or 7 set, and sorts the actors by key, highest first; an exchange needs a strictly higher key, so ties keep the order Benjamin, companion, first, second and third monster. A round after a first strike or a failed run includes only one side (ffmq/first-strike, ffmq/run). ffmq/turn-order

About: Final Fantasy Mystic Quest Turn order

Speed is offset $24 of a battle record, where the loaders put the current speed (ffmq-tables/monsters, ffmq-tables/characters). The key is 8 bits.

The main loop runs the run check when bit 6 of $1020, in Benjamin's record, is set; what sets that bit isn't read. The run fails outright when the formation's flags byte has bit 6 set, and succeeds outright in round 0 after the party won the first strike. Otherwise the game takes the party's speed (Benjamin's, averaged with the companion's when both can act) and the monsters' average speed: the speeds of those that can act, summed from 1 instead of 0 when the first monster can't act, over their number. It draws a random byte modulo ⌊average ÷ 5⌋ × round + 1 (rounds counted from 0; the product and the + 1 kept to 8 bits), and the run succeeds when (average − draw) mod 256 is below the party's speed, so a draw larger than the average wraps to 256 + average − draw. A failed run gives the monsters a round to themselves. Computed: in round 0 the draw is 0, so the run succeeds only when the party is faster. ffmq/run

About: Final Fantasy Mystic Quest Fleeing

"Can act" is the status byte (offset $21) having bits 4-7 clear. With no monster able to act the division is by 0; with no party member able to act the party's speed is 0 and the run fails. When ⌊average ÷ 5⌋ × round is 255 the + 1 makes the range 0, which leaves the random byte whole (ffmq/rng).

After a won battle, each monster present adds 3 times its experience byte to the battle's experience and 3 times its gold byte to its gold (ffmq-tables/monsters). The code would use 6 for a gold byte of $42-$49 and 10 for $4A or more, but no monster's gold byte is above 10. ffmq/battle-rewards

Value: multiplier 3

The test compares the gold byte with $42, the first number of the bosses' range in the monster table, which suggests it was meant for the monster number; as shipped it never fires.

When Benjamin's experience reaches the figure at $0510, he goes up one level, to at most 41: his maximum HP rises by 40 and his current HP is scaled by the new maximum over the old; his maximum white magic rises by 1, black by 1 whenever half his level (rounded down) rises, and wizard whenever a quarter of it does; his level stats rise by 3 attack, 2 defense, 2 speed and 1 magic, and offset $40 becomes 75 plus half his level. The check runs once after a battle's rewards and once after a battlefield's experience reward. ffmq/benjamin-level-up

Value: cap 41 · hp 40 · attack 3 · defense 2 · speed 2 · magic 1 · offset 40 75 + level/2

The four stats at $1026-$1029 are clamped to 99 before the level stats are copied over them, so the clamp doesn't limit the new values. Companions don't go through this routine: they arrive with a record's fixed level (ffmq/companion-records).

Cited by: Growth rate

A companion joins when an event-script command names one of the 9 character records (ffmq-tables/characters): the game copies all 80 bytes of that record over the companion's place at $1080, so the companion arrives at the record's level, HP, stats and equipment, and nothing of the previous companion's record is kept; bit 7 of offset $20 is cleared in the copy unless it was set in the record it replaced. ffmq/companion-records

Each companion has two records, for its first and second time in the party, at levels 3 and 31 (Kaeli), 7 and 23 (Tristam), 15 and 34 (Phoebe), and 23 and 31 (Reuben).

A save holds three blocks: Benjamin's 80-byte record at $1000, the companion's at $1080, and the 380 bytes at $0E84-$0FFF. The routine at $00:C9D3 copies them, in that order, to the start of a buffer at $7F:3000 (540 bytes), and the routine it calls three times writes the buffer's first 902 bytes (what fills the last 362 isn't read) to save RAM in bank $70, after a 6-byte header that holds a checksum of them, at slot × 908 for slots n, n + 3 and n + 6, reading each copy back to check its checksum. Loading copies the three blocks back from the buffer and then runs the same save. A new game fills the blocks from the cartridge: Benjamin's record from the character table, $FF in the companion's level and status, and the 380 bytes from $0C:D380, which put each battlefield's count of 10 at $0FD4 (ffmq-tables/battlefields). So each battlefield's count, which a won battle there lowers and a cleared one leaves at 0, is in the save. ffmq/save-contents

How Final Fantasy Mystic Quest computes physical and magic damage hasn't been read yet. ffmq/damage-formula

About: Final Fantasy Mystic Quest Damage formula

Cited by: Damage formula

How the game decides whether an attack hits hasn't been read yet. ffmq/hit-chance

About: Final Fantasy Mystic Quest Hit chance

Whether and how the game rolls critical hits hasn't been read yet. ffmq/critical-hit

About: Final Fantasy Mystic Quest Critical hit

The shops' stock and prices and the chests' contents haven't been read yet. ffmq/shops-and-chests