This game has the same exact Cx4 test that Mega Man X2 does, and it's even activated the same way. Hold "B" on controller two, then turn the game on. It doesn't affect gameplay, it's just a developer's tool.
Unused Ganseki CharacterEdit
This type of Ganseki Carrier isn't used in game. It flies back and forth with a large spike ball and will fire at X/Zero when they're in range. Unlike the other types of Ganseki Carrier that eventually drop what they're holding, this type does not. When you kill it, the spike ball drops to the ground. The ball reflects all shots and damages you, as expected.
Video footage can be seen here from 0:00 to 0:18.
Unused Wild Tank BehaviorEdit
The Wild Tank enemy is digging out of the ground in this screenshot. This type of Wild Tank is initially invisible. When the player comes close enough, the wild tank "digs" upward, creating a dust cloud. The enemy moves up by 12 pixels. In the final game, all Wild Tanks appear above ground by default.
Video footage can be seen here from 0:18 to 0:36.
Unused Vertical Boss DoorEdit
An unused set of vertical boss doors found above Blast Hornet's boss room. The tiles obviously have not been loaded properly. Maybe you originally dropped into his room?
Video footage can be seen here from 0:37 to 0:57.
The back of the Mega Man X3 box sheds light on the mystery to this one! At one point, it was indeed possible, or at least planned, to drop in on Blast Hornet via the ceiling! Where it's positioned, it is rather strange, because nowhere else in Mega Man X3 does the game ever have you drop in from above on a boss. Also, since Blast Hornet enters via the same area, it would have looked rather strange. An understandable deletion on this one.
A very odd boss that's completely unused in the game. It drops from the top of the screen until it hits the floor. Despite the fact that it flashes when you hit it, it has no invulnerability time.
The only explanation I can come up with is that this object was used to test the Ride Armor's different animations and its health bar.
Video footage can be seen here from 0:57 to 1:36.
(Source: GoldS) Bold text