Bugged special attack

[YinYin]

- The wave hits, but the opponent sometimes flyes towards the wave instead of being thrown back by it

Sounds a lot like an explosion effect (direction depending on the hit objects position). You don't seem to have any of that in your data and the problem doesn't occur when loading it in another game so we have to assume you broke your loading sequence on the game that has the problem somehow.

Are both game data.txt files clean (loading no other custom data except this character)? Also are you loading both in the same spot (same objects order inside the data.txt)?
Do you use a certain id?
In my experience you can easily achieve some stack overflows by trying loading too many things (bitmaps/object, itrs/frame). The overflow is then written into the next slot of the games memory - which could cause these itrs to have effect 23. (this stuff isn't strictly limited to a single object - it can also happen due to loading problematic objects in a certain order - changing it can sometimes fix things)

Does the problematic itr play a burning sound when hitting someone backwards? Could you check out the itr effects with the AI debugger?

- I set vrest: 90, but the wave often hits multiple times anyway

Very high vrests often don't correspond to how you would expect them to scale up from the line up of lower values (see vrests on freeze whirlwind for example: 100 and 200). Better use something like 25.