A malevolent fusion of Sonic and Shadow created by using the negative energy of the Chaos Emeralds, Seelkadoom is the culmination of Dr. Gerald Robotnik's research. Menacing and cruel, he seeks to sieze control over NiGHTS' dimension through any means necessary. In addition to the powers he gained from Sonic and Shadow, he also gained their skills with Extreme Gear, making him a force to be reckoned with on the track.

"It seems that lightspeed just isn't enough to beat me."