Scrap Elf

Scrap Elf (プアエルフ) is the corrupted Cyber-elf enemy in Mega Man Zero 4 that appears in the Hibernation Chamber, Fenri Lunaedge's stage in capsules that shatter when you get too close. They enter in Pantheon Corpses to reanimate them. Scrap Elves can only be defeated by taking Lamps with the Zero Knuckle to push them to the light in the end of the area they appear. Because of this, Scrap Elves are invincible in Hard Mode, where there is no sunlight to kill them.

Trivia
There is a mini game that involves using a lamp to drive a Scrap Elf to sunlight at the end of the area.