Invisibility 
Do the following sequence whilst in the pause menu: Trigger-R, Trigger-L, D-pad-R, D-pad-L, D-pad-R, D-pad-L, D-pad-R, D-pad-L, Button-Y, Button X, Button X, Button X, Button X, Trigger-R, Trigger-L. To make the robots normal again, just enter the cheat once more. 

House Robots:
Press R, L, Up(3), L, R, Down(3), X at the competition mode menu to unlock the House Robots in arcade mode. 

Dominator 2, Tornado, and Chaos 2:
Successfully complete stage 7 in competition mode and defeat the champion to unlock Dominator 2, Tornado, and Chaos 2.

Hypno-Disc and Razer:
Successfully complete stage 6 in competition mode and defeat the champion to unlock Hypno-Disc and Razer.

Extra Money 
Go to the competition mode menu and input the following button sequence: L, R, L, R, Y, X, D-Pad Up, D-Pad Left, D-Pad Up, R, L, R.