ULTIMATE MARVEL VS CAPCOM 3

For those they find it difficult to get first attacks then i would suggest that you go to arcade mode and set the options to very easy . The enemy is really idle on this difficulty and there is a higher chance to get the first attacks.

I also suggest to pick sentinel and spam his heavy attack (B) that projectiles a beam without an effort ;)

Good luck.

To get a First Attack, simply attack your opponent at the beginning of the match before he ever hits you. Do this 50 times and you're done. Very Easy.