[poccil]

RBG:

1) My guess is that Custap Berry has no effect when it is consumed due to Bug Bite, since it doesn't work the same way as Oran Berry, Persim Berry, and the like, since it has no effect during the so-called "berry checks", but rather at the beginning of each round. I am not sure about this, though.

UPDATE: I was right. Custap Berry has no effect in that case.

2) When does "Pokemon A" begin to have 25% health? If it was at the beginning of the round, the Custap Berry had "activated" and will be consumed at the beginning of the holder's turn. Maybe the question is whether that item is consumed from the holder who caused the berry to activate.

UPDATE: I've discovered something interesting. When Trick is used on a Pokemon on the same round that a Pokemon's Custap Berry is activated, but before that Pokemon's turn, the game still displays the message "[Pokemon]'s [item] let it move first!" as that Pokemon's turn begins, where [item] is the Pokemon's new item after Trick was used. However, the Custap Berry itself is not consumed, since the Pokemon is no longer holding it. (This happens because the priority is determined just after all commands are chosen for the round.)

3) UPDATE: If the holder of Custap Berry strikes second or third but not last, the Custap Berry is still consumed.

Tri Attack:

My description for Tri Attack reads: "May either burn, freeze, or paralyze opponent." Thus Tri Attack can't cause more than one status problem simultaneously, but chooses one of the three.