Two words: counter-attacks. Most nonboss enemies who come in bunches are easily killed with minimal health lost by doing counter-attacks. I used to think the exploding green ninjas were impossible, but if you block their explosions and they get close, simple block x/y counter attack will kick the shit out of them.

The Y counter attack is the best to use when surrounded by enemies.

you can use the double x counter to kick people off ledges, most ledges their kicked off of will kill them. It's funny too.