Level select cheat:

D-L-D-R-D-U (D=down, L=left, R=right, U=up)

do this at the menu screen and you'll see all the levels pop-up

     There's some in game cheats, but I couldn't find what all of them
did.  All  the  cheats  are  Up-Up-Up and then a combination of Slash,
Block, and Jab.

     I  think  the most useful is uuubbb which moves your strength and
endurance meter up a notch.