Chaos Devil

The Chaos Devil is a creature made by Dr. Eggman and Dr. Wily in the Sonic the Hedgehog and Mega Man crossover event, Worlds Collide. A combination of Chaos from Sonic Adventure and Yellow Devil from the original Mega Man video game, it is essentially a monster created by the two scientists.

History
Unknown how the monster was made nor how Chaos was brought up to this form, it was purposely released by Rouge the Bat inside the Wily Egg to distract Bass and Metal Sonic from capturing her while she was finding the weak points on the Wily Egg. The Chaos Devil, unknown who is friend or foe, attacked the three and had successfully captured Rouge and Metal Sonic. However, Dr. Eggman and Dr. Wily came in and Eggman berated Chaos Devil and told him to put Rouge and Metal Sonic down just as if Chaos Devil was a dog. The monster-hybrid did as Eggman told it to and Eggman and Wily were able to know the Chaos Devil functions well that they had expected. (SU #53)

Trivia

 * Chaos Devil is essentially a Yellow Devil body covered with Chaos' liquid.