Evil Energy

Evil Energy is an alien energy source that first appeared in Mega Man 8. Usually, it looks like a swirling purple flame in the shape of a skull. The energy absorbs evil within a person's mind and then multiplies to infect others--mainly robots, in the case of the game. Duo hunts down this energy to stop it from infecting the whole universe.

In the opening of Mega Man 8, Duo is seen in space, battling an evil-looking robot utterly consumed by the Evil Energy (it is unknown if this is another victim of the Evil Energy or an actual manifestation of the energy itself). He manages to defeat the robot, but both combatants fall to Earth, impacting a remote island. Unfortunately, the island happens to be Dr. Wily's secret base, allowing the mad scientist to discover the remaining Evil Energy. He escapes with his prize as Mega Man shows up, and eventually learns how to harness its dark powers.

Using the Evil Energy apparently allowed Wily to power up his robots and construct a massive new fortress in the heart of a volcano. His first four Robot Masters carried capsules of Evil Energy in their bodies, although it isn't known if it had augmented their powers or bad personality, or was simply a power source.

When the first capsules of Evil Energy were collected, Mega Man brought them back to Dr. Light in hopes that his creator could analyze them. However, Duo, having been brought to Light's laboratory for repairs, sensed the Evil Energy and destroyed it before breaking out and heading for Wily's tower. Pursuing the mysterious robot, Mega Man also arrived at the tower, only to be attacked by a massive robot powered by Evil Energy. Duo arrived and destroyed the robot with a single blow, before explaining the properties of Evil Energy to Mega Man. Since Duo had to leave and scour the world for traces of Evil Energy, Mega Man infiltrated Wily's fortress to stop his experiments with Evil Energy. Along the way, he was forced to defeat Bass, who had used the energy to power himself up and fuse with Treble.

When Mega Man destroyed Wily's final machine, the Evil Energy within it suddenly entered his body in an attempt to corrupt him. Duo spirited him away from the crumbling castle and managed to purge Mega Man of the energy through a combination of his own abilities and Mega Man's own will. With the last of the Evil Energy destroyed on Earth, Duo left to find other worlds where the dark power had manifested.

Evil Energy makes a minor appearance in Duo's ending of Mega Man 2: The Power Fighters, where he comes to Earth in search of new sources that have appeared since his last appearance. After defeating Dr. Wily, he collects the energy before leaving once more.

This energy was the basis for the Maverick Virus, according to Rockman Zero Collection official site. (Translation in The Mega Man Network).