Everytime i try to copy anti-venom 2 for Tidus it never successfully works! Tidus level is 35 and im trying to copy from 20-25's. Why wont it work?!?!?

Did you get Tidus's first two key abilities?

If you did, make sure he's marked with the player who's using Anti-Venom 2. Then, when you have a character use a Venom Tackle, Venom Pass, or Venom Shot (if it's a goalie), then press [x] right when a green circle is around the player with Anti-Venom 2, a little bit after the sound that indicates that the player is not inflicted with the status.

If you don't have Tidus's first two key abilities, he can't learn Anti-Venom 2. Well, unless you used a Tech Find on the space.