Mikhail Rasputin was first mentioned in X-Men (1st series) #99.
Mikhail's power has always been rather nebulous. He has been seen firing destructive blasts and teleporting through space and dimensions. Mikhail was the first to show Iceman his full potential by transforming Bobby into living ice for the first time. Throughout his time on "The Hill", Mikhail was influenced by a symbiotic energy signature. It was divested from his system in Uncanny X-Men (1st series) #374.