Rareware Online has tested all of the following codes and cheats. We guaruntee that each and every one of them works. If they don't work, you're doing something wrong. If you're doing everything we said and it still doesn't work, we obviously did a crappy job of explaining it, so tell Marc about it.

Rainbow Blood
Collect 100 enemy heads.

Jet Force Kids
Collect 200 enemy heads. Note that these aren't the original Juno and Vela character models. They're just kid-sized versions of the normal characters.

Ants as Pants
The coolest code by far. Collect 300 enemy heads for this one. All normal blue ants (without shields) will turn into the popular Mr. Pants of rareware.com fame, a poorly-drawn fat man created by Rareware's Mr. Loveday.