what happen when he win a I challenge?

That's a lot of work to make that happen....

In the end, you have conflicting replacement effects, so the First Player decides which one is the final effective one for replacing claim. (If you really want to know the mechanics, I'll spell it out, but the end result is that the First Player decides whether the "choose and kill character" or "choose and discard card" effect wins out.)

I would assume that the first player decides which of the conflicting Replacement Effects would be used.

the anwser that "the first player decides" is enough