Toitank

Toitank (トイタンク) are small gun enemies in Mega Man Zero 2 that shoot at Zero while riding on tracks on Phoenix Magnion's stage. There are three different colors of it, each with a different speed. If the player defeats all of them before they dissappear, a U4 will appear.

U4
U4 is a robot that appears after all Toitanks have been defeated. It contains a Cyber-elf.