What you do is hold the A button down to fill the attack meter, each of your 4 attacks are done by filling up 1/4 of the meter. 1/4 meter filled is attack 1, 1/2 filled is attack 2, etc.
You hold A down to fill the meter, then you release and (I think) you press B to choose an attack. The attacks you can pick from will be highlighted as your meter fills up.
It's stupid because if you're content with picking the 1st weak attack, you can always attack before the opponent. The SNES version had a moving bar, kinda like when you defend on the MD one, and you tried to press A when it landed on a certain spot to initiate an attack.