The Dishwasher Dead Samurai

With the meat cleavers on the first level. You'll be told how to hit enemies in the air using x, x, x, DOWN and x. Then in the air hold up and press x, to do a wall slam. Keep holding up and pushing x, to do loads of slams.

Easy Ach.

You can unlock this in any level with a few enemies, but I think it´s easier on Arcade mode. Just play one of the first levels, and keep pressing X and Y. When you end the X, X, X, X combo, you will launch enemies forward, and they will hit the wall. You can do it with Y too.

If you look at your right, you will see how much time do you have until the combo ends. Keep hitting them before it runs out, or the combo will end, and you´ll have to start it over.

Anyway, it´s easy to get it soon after starting to play this game.

It's actually really easy once you get the Arsenal. Just keep hitting the Y button until it pops. The shotgun blast counts as a wall slam if you are close enough to a wall.