When in the Ice stage in two player mode, use the Spider and get the upside-down item. Go to the far end and go to the lift. Move back a bit and use the upside-down item to reach the highest point of the level. You should see a few dots. Land on top of it and you will be standing on them. This will not work with any more warriors.
Successfully complete the game, then return to the main menu. A ???? option will be unlocked. This is a special head-to-head mode where play one is in a nitro. Player two is a ballistic, but shaped like a basketball, with what appears to be a programmers head inside.
Successfully complete level 7 without using any continues up to that point.
Press A when close to an opponent.