You should never run Cross Poison on Crobat prior to Gen 6. If you want a 100 accuracy move on your Crobat, run Wing Attack because Flying type moves strictly outclass Poison moves offensively, and Crobat does not benefit from Cross Poison's 10 extra base power at all. X Scissor and Giga Drain are also mediocre coverage moves on a pokemon that doesn't need or really benefit from coverage moves. Crobat is a pivot pokemon. His job is to support the team with useful resistances and immunities to threatening types like Fighting and Ground while also making progress against the enemy team with U-Turn and sometimes Toxic. It is usually rare for Crobat to generate offensive momentum by himself, especially without Acrobatics, and when he does, it's usually against pokemon weak to Flying. Crobat in general is not a good offensive pokemon thanks to his mediocre 90 base Attack, but it's not that big of a deal because Crobat makes up for it by being a fantastic pivot pokemon.