Master Overlord

Master Overlord is a transformation that appears in the Sonic the Hedgehog comic series published by IDW Publishing. It is the final transformation of Neo Metal Sonic, achieved through powering up with the combined power of Sonic and Shadow's biodata, as well as the Master Emerald.

The Battle for Angel Island
After being forced out of his Super form by Shadow the Hedgehog, Neo managed to copy Shadow's biodata in the process. Combining his biodata with Sonic the Hedgehog's, Neo once again powered up with the Master Emerald and fused with his own fortress to become Master Overlord.

Trivia

 * Master Overlord is quite similar to Metal Madness and Metal Overlord from Sonic Heroes, even to the point of having a similar name with the latter.