To access this test, hold "B" on Controller 2, then power the game on. It doesn't change anything gameplay-wise, since it was a developer's tool.
Ride Armor EnemyEdit
While this isn't actually an "unused" enemy, the way the game lays out Wheel Gator's level, you won't usually see these guys. You have to actually be out of the ride armor for these guys to load up and appear, so you'll have to typically do this on purpose. When they see you, they'll jump into the ride armor. If you get in it before them, they'll start shooting you!
Video proof can be seen here.
(Discovery by: GoldS)
(Video by Rick L)
(Sprites ripped by Sprites INC.)
There appears to be an test enemy, according to GoldS:
This is the object with ID #1. It always loads the large weapon refill graphic. From the first orb, seven more orbs are created downward. The first orb is the anchor. Each orb moves seperately, except the anchor orb, which doesn't move at all. Together they move in a wave like motion in the direction of X. This object has HP and can be destroyed. The anchor sphere is the first to be destroyed, followed by the connecting spheres.
A video of the enemy in action can be seen [here].
Unused Enemy BehaviorsEdit
As is shown in the five pictures above, all five of these enemies have behaviors where they are upside-down. No idea why they were included or cut, though it seems likely that some of the enemies would attack from or stick to the ceiling.