Null

 Null is a virus from the Mega Man Battle Network series. It moves around slowly on its side of the battlefield. However, when it goes to attack, the virus will appear in front of its target to punch. It heals itself over time and can change two panels on the target's side to whirlpools, each causing 200 damage. If the target is behind an obstacle, the virus can push the obstacle into the target, damaging the target.

Null
 Nulls are blue with white eyes.

Void
 Voids are purple with green eyes.

Null&Void
 Null&Voids are black with red eyes.

Source
Sprite images found at Sprites INC