Type in these cheats on the pause screen-
BIG GUN-X(x4),Y(x3)
EXPLOSIVE CROSSBOW-Left,Right(x2),Left,X,Y,R button,L button,X,Y,Left,Right.
EXPLOSIVE SNIPER-R button, L Button, Right,Right,Left,Left,Right(x2),L button
HALF DAMAGE-X,X,Y,Y,Left,Left,Right,Right,Y,Y,X,X
LEVEL SKIP-R button,X,R button,Y,R button,Left,R button,Right,R button,L button(x2),X,L button,Y,L button,Left,L button,Right,X