[Error] This held item's simple code should increase speed by 1 on Switch-In, so why does it crash or prevent the game from starting?

[SuperSpyroDragon64]

My game's either allowing me to play until I send out a Pokemon holding the AD18 which causes a crash, or the game refuses to start and puts up error messages playing the "sorry ) should be a } haha I mean ] haha I mean ) I mean too many )s I mean not enough )s" cycle with me no matter how I change the code. Sometimes changing the code lets me get into a battle, only for sending a Pokemon out holding the AD18 item to cause crashes. The error messages given say it doesn't know what I mean by "Item" if it doesn't just whine about the number of "{{]])end)"s

This held item is just supposed to raise Speed by +1 when sent out. Like the "Intrepid Sword" ability but as an item that boosts Speed.

BattleHandlers::ItemOnSwitchIn.add(:AD18,
  proc { |item,battler,battle|
    battle.pbDisplay(_INTL("{1} gained 1 Speed stage from the Drive!",
      battler.pbRaiseStatStageByCause(:SPEED,1,battler,itemName))
  }
)

 

[StCooler]

My game's either allowing me to play until I send out a Pokemon holding the AD18 which causes a crash, or the game refuses to start and puts up error messages playing the "sorry ) should be a } haha I mean ] haha I mean ) I mean too many )s I mean not enough )s" cycle with me no matter how I change the code. Sometimes changing the code lets me get into a battle, only for sending a Pokemon out holding the AD18 item to cause crashes. The error messages given say it doesn't know what I mean by "Item" if it doesn't just whine about the number of "{{]])end)"s

This held item is just supposed to raise Speed by +1 when sent out. Like the "Intrepid Sword" ability but as an item that boosts Speed.

BattleHandlers::ItemOnSwitchIn.add(:AD18,
  proc { |item,battler,battle|
    battle.pbDisplay(_INTL("{1} gained 1 Speed stage from the Drive!",
      battler.pbRaiseStatStageByCause(:SPEED,1,battler,itemName))
  }
)

I mean. The error message for this is explicit. It tells you that "itemName" is not defined.
You need one more line to define itemName as:

itemName = GameData::Item.get(item).name

Anyway, that's not the only mistake I see; only this one is causing the crash. When you solve it, there will be other errors.

1. The function embedding as you do it will not display the name of the Pokémon. The function battler.pbRaiseStatStageByCause(:SPEED,1,battler,itemName) will return a boolean value, basically stating whether the increase happened or not. Thus, you should separate both functions.
2. So how do you get the name of the Pokémon? You should use battler.pbThis.
3. But, actually, the function pbRaiseStatStageByCause already displays the annotation, so you don't need to write it.
4. There is one more thing you should consider. Actually, in Essentials, you should check if you can raise the stats of the Pokémon, before actually doing it.

In summary, your code should look like this:

BattleHandlers::ItemOnSwitchIn.add(:AD18,
  proc { |item,battler,battle|
    if battler.pbCanRaiseStatStage?(:SPEED,battler,nil,PokeBattle_SceneConstants::USE_ABILITY_SPLASH)
      if PokeBattle_SceneConstants::USE_ABILITY_SPLASH
        battler.pbRaiseStatStage(:SPEED,1,battler)
      else
        itemName = GameData::Item.get(item).name
        battler.pbRaiseStatStageByCause(:SPEED,1,battler,itemName)
      end
    end
  }
)

Something else. Your item ID is "AD18", but you mention "Drive" in your text. I assume your item is called "American Drive 18" (I am joking about the "American" part), so your item ID should be "AMERICANDRIVE18". This is because when you will be debugging your code in 20 months (I am not joking or overestimating), you will likely waste time remembering what item is "AD18".
Now for one item there should be no problem, but now assume you have 31 items, 64 moves, 18 abilities and 32 effects; it becomes mind-consuming.

 

[SuperSpyroDragon64]

American Drive! Funniest thing I've heard in ages. In truth I only plan to have a handful of these ADs with a pinned wordpad text file to remind me which one does what. I also have a reminder of each one's intended effect commented out near the name.

Speaking of these ADs, does the engine support turning this modified ability into an item? When I tried changing BattleHandlers to BattleHandlers::TargetItem that caused crashes.

BattleHandlers::MoveBaseTypeModifierAbility.add(:AERILATE,
  proc { |ability,user,move,type|
    next :FLYING
  }
)

I intentionally removed the power boost and "Is this normal?" check from Aerilate to match my other -ate and -ize abilities, I made a new one up for each type and I was hoping to make items that do the same thing.

 

[StCooler]

American Drive! Funniest thing I've heard in ages. In truth I only plan to have a handful of these ADs with a pinned wordpad text file to remind me which one does what. I also have a reminder of each one's intended effect commented out near the name.

This is exactly what you shouldn't do.
You shouldn't have an intermediary, a converter from what you see (your ID) and what you want (the item). Make coding easier for you.

Speaking of these ADs, does the engine support turning this modified ability into an item? When I tried changing BattleHandlers to BattleHandlers::TargetItem that caused crashes.

BattleHandlers::MoveBaseTypeModifierAbility.add(:AERILATE,
  proc { |ability,user,move,type|
    next :FLYING
  }
)

Actually, right now, the only Battle Handlers that change types of moves are abilities.
Check out the class PokeBattle_Move, and in particular this function:

  def pbBaseType(user)
    ret = @type
    if ret && user.abilityActive?
      ret = BattleHandlers.triggerMoveBaseTypeModifierAbility(user.ability,user,self,ret)
    end
    return ret
  end

You will need to adapt all the code from BattleHandlers.triggerMoveBaseTypeModifierAbility(user.ability,user,self,ret) to Battle Handlers. It's not difficult but it will require a bit of coding.

I intentionally removed the power boost and "Is this normal?" check from Aerilate to match my other -ate and -ize abilities, I made a new one up for each type and I was hoping to make items that do the same thing.

Now, your code means that any Pokémon with Aerilate, should convert any move of any type, to the Flying-type? (this is what your code does, right now).

 

[SuperSpyroDragon64]

Aerilate (and all other -ate and -ize abilities) in my game convert any move the pokemon with the ability uses into the -ate ability's type. So Aerilate makes everything used by the Pokemon Flying type, Incinerate makes its moves Fire type, and Burninate makes its moves Dragon type. There's one ability per type right now, and I thought about adding a QMARKS-type ability called Obfuscate but since there are no ??? type pokemon this would mean no STAB, and if it did get STAB as a side effect of the ability, its unresisted attacks would be too strong on a setup sweeper with a wide movepool. So far this works in ability form, now I want to make held items that function the same way but fail if a -ate ability is active. I'll give the Drives better individual names when I think of some.

def pbBaseType(user)
  if !user.ability == :NORMALIZE
  ret = @type
  if user.item = AD1
#    ret = :NORMAL
      ret = BattleHandlers.triggerMoveBaseTypeModifierAbility(:NORMAL,user,self,ret)
  end
  return ret
end
  end

I tried but the code didn't work with ret=:normal or the other thing.