Effects of abilities, IQ skills and held items

[Metalcape]

Unlike moves, passive effects like abilities and held items do not seem to have a specific piece of code that implements them. Instead, they are just flags in an entity that the code checks when performing certain actions. Abilities like Klutz are all over the place, because whenever the effect of a held item needs to be applied the code also checks for Klutz. On the other hand, others are checked only in a specific instance, for example those which can only activate at the end of a turn (like Speed Boost or Shed Skin). There are also some which do have their own functions, both very simple (like Truant which just tries to apply the pause status) and very complex (like Forecast which has to manage multiple form changes).

Given these inconsistencies I feel like the best course of action would be to search for calls to AbilityIsActive, IqSkillEnabled and CanUseHeldItem (this is a name I decided for the function at 0x022E3CBC which checks for Klutz and then calls HasHeldItem) to see where the code checks for skills, abilities, and items, and then start reversing the functions containing those calls. This is what I'm currently trying to do, at least for abilities.

Relevant addresses
All of these have been found in the EU version of the game.

• 0x022E3CBC bool CanUseHeldItem(entity*, item_id): Checks if the entity holds an item and does not have Klutz. Also at 0x022EECC8, 0x022F6350 and 0x02311A94
• 0x022E9FA4 bool EntityIsNotNull(entity*): Returns true if the entity is not ENTITY_NOTHING. Used in many different places before checking parameters of an entity. Also at 0x022F7D1C, 0x022FA12C, 0x0230248C, 0x0235FB8, 0x02308924, and 0x02311A70
• 0x022EBB28 TrySwitchPlace(entity* user, entity* target): Attemps to switch places between user and target, checks for Suction Cups and Mold Breaker
• 0x022ED08C: Probably the function that applies the effect of Plus and Minus
• 0x022F9C48: Function that triggers Slow Start, takes no parameters and returns nothing. Probably called at the start of the floor and checks all pokémon
• 0x022F9CE4: Function that triggers abilities that change the weather. Also returns nothing and takes no parameters
• 0x022FA0D8: Returns the result of AbilityIsActive on an entity if another entity does not have Mold Breaker, otherwise returns false
• 0x022FA1FC TryAbilityTruant(entity*): Tries to inflict the pause status if the entity has truant
• 0x022FEEDC: Long function that checks for Mobile Scarf and the Absolute Mover skill, might be related to checking the type of tile an entity is moving into
• 0x02300988: A function that checks for Unburden, Chlorophyll and Swift Swim and returns 1 or 2, which I assume is the number of times a move has to be used
• 0x02302844 bool IsLevitating(entity*): Checks if an entity is levitating (has Levitate and there is no gravity)
• 0x02310604: A function that checks for the No-Slip Cap and probably tries to make a random item sticky
• 0x02310698: Another long function. This one seems to check for many items and abilities that would trigger at the end of a turn, such as the Warp Scarf, things related to belly drain, abilities triggered by weather like Sand Veil, abilities connected to status effects like Poison Heal and Magic Guard, and also Speed Boost. I think it also does many other things unrelated to abilities/skills/items
• 0x02311A38: A function that checks regen-related effects like the Heal Ribbon and the Quick Healer skill. Probably modifies the amount of HP regenerated per turn.
• 0x02335BB0: Probably the function that applies the effect of Forecast and changes Castform's forms

For now the information I've found is very incomplete, so I decided to open this issue before making any contributions. I'm new to reversing this game and I don't know if there is a better way to research this, let me know if I'm missing something.

[UsernameFodder]

Thanks for this, there's already a lot of great information here, even if it's incomplete! Feel free to make small PRs with incremental changes as you figure things out; that's what the repo is designed for. Symbols don't have to go in all at once.

Some thoughts:

• A couple of these small utility functions sound like existing functions in the repo (although currently the addresses are predominantly NA).
  • CanUseHeldItem sounds like ItemIsActive?
  • EntityIsNotNull sounds like PptrIsValid (although perhaps if this is only used with entity pointers it might be useful to rename it)?
  • The function at 0x022FA0D8 that checks for Mold Breaker sounds like DefenderAbilityIsActive?
• For the functions that are repeated in a bunch of places, perhaps arm5find.py in the tools/ directory might be useful in identifying all instances. You can use it to search for identical chunks of assembly throughout a binary.

[Metalcape]

Thanks for the suggestions, I've looked into those duplicates and yes, they are the same functions, I ended up renaming them because those instances I found had no symbol assigned so I didn't notice there were duplicates that already had a name. Also I forgot to specify that all those addresses come from the EU ROM, so I added that to the first message.
I set up another Ghidra project for the NA ROM and there I found something interesting about the functions checking entity pointers:

• What I called EntityIsNotNull is in fact PptrIsValid, and I've only ever seen it used on entity pointers (so far). I've found something like 30 copies of it inside overlay 29 using the arm5find script, while in the symbols there is only 1 for EU
• It turns out that I made a mistake, and some of those EntityIsNotNull addresses are actually a slightly different function, which in NA symbols is called IsMonster (unnamed in EU). The only difference is that while PptrIsValid checks for the pointed value to be different than zero, the other checks if the pointed value is equal to 1. In the EU ROM the addresses I found for IsMonster are 0x022FA12C and 0x0230248C.

I think for now I'll check these duplicates and try to add all the copies I find to the symbol files, since they will be useful to have once I get to the longer functions

[Metalcape]

PptrIsValid seems to be called on a pointer like this most of the time:

*(int **)(*(int *)PTR_DUNGEON_PTR + localVar * 4 + 0x12B28)

Sometimes Ghidra interprets the (int **) pointer as (entity **). If those addresses contain entity data we should consider renaming the function. The NA symbols already have some duplicates of it under the name EntityIsValid

EDIT: I checked the dungeon struct trype and that offset is in fact named entity_table, unfortunately Ghidra is bad at correctly interpreting the double pointer which should be ((*PTR_DUNGEON_PTR)->entity_table).header.monster_slot_ptrs[localVar] when applying the type dungeon** to PTR_DUNGEON_PTR

[Metalcape]

I'll drop here some more symbols that I found but still need more research on what they actually are. (All addresses are EU)

First, some functions not strictly related to effects, but which are probably responsible for deciding the order in which different events happen in a turn:

• 0x22EC698: This looks like the function that runs each (fractional) turn. It is called in a loop about halfway through InitializeDungeon which uses the return value from 0x22ED198 (see below) as condition. At the end, increases the fractional turn counter and resets it to 0 if it reaches 0x18.
• 0x22ED198: Returns true or false by checking the two flags related to climbing stairs, but also sets another unknown flag to 2 if the climb stairs flag is 1 or 2.
• 0x22ED08C does more than just writing the plus/minus flags, it also calls 2 complex functions. One at 0x230F130 seems to manage the spawn counter, the other is at 0x22E0F60 and I still don't know what it does, except it seems to be related to field 0x14 in the dungeon struct (unknown).

Functions related to specific effects:

• 0x22FA8AC: Related to belly drain, checks for items that increase it.
• 0x2300820: Calculates the speed level from speed up/down counters, takes snowy weather and the IQ skill Time Tripper into account. Has a second int parameter which apparently acts as a multiplicative "weight" for the value of each speed counter?
• 0x22FC124: Seems to apply the effect of Brick Tough and Multitalent

And finally an interesting data label: at 0x2352E90 there is an array of short that is accessed in multiple functions using the fractional turn counter (or some manipulation of it) as an index. For example 0x22ED08C accesses it using fractional_turn * 2 and then returning if the value equals zero.