The Wisps are a species of small, tentacled aliens that possess some kind of unusual power.
During a previous adventure, Sonic and Tails (with the aid of a Wisp named Yacker) once rescued the Wisps from being enslaved by Dr. Eggman who wanted to harness their Hyper-go-on power. The full details of how they defeated Eggman and saved the Wisps is unknown, except that it apparently involved Silver the Hedgehog. (StH: #252)
The above events are also known to have occurred in some form in the past of the altered timeline created by the second Genesis Wave. Sonic briefly mentioned them to Mega Man, and remarked that he'd be curious to see what he could do with one. (MM: #27)