These abilities were supposedly further enhanced by Onslaught when Rankin and Blob encountered X-Force.

In his first appearance he permanently gained the ability to use the powers of the original X-Men and Charles Xavier:
Angel's wings
Beast's physiology including enhanced strength and agility
Cyclops' optic blasts
Iceman's cryokinesis
Phoenix's telekinesis
Professor X's telepathy

When interacting with normal humans, Mimic will imitate their skills, personality traits, and intelligence. Thus, when in the vicinity of athletes, he gains superior athletic ability. Also, when in the presence of a scholar, not only does his knowledge expand, but so does his potential to learn (I.Q., E.Q. etc...)

When Calvin copies the abilities or powers of others he doesn't copy a persons flaws (Ex. When Cyclops was young he received a bump on the head which allowed him to not control his powers. However Calvin can control Cyclops' optic blasts).

The number of powers or people he can mimic are unknown or if he can keep the powers he copies indefinitely. He has been shown to be able to copy the abilities of over 10 people at once. Calvin has copied the powers of Banshee, Douglock, Wolverine, Marrow, Gambit, Rogue, Storm, Colossus, Nightcrawler, Shadowcat, Captain Britain, Feron, Meggan, Kylun, Micromax, Captain U.K., Marvel Girl (Rachel Summers), Wolfsbane, Peter Wisdom, Psylocke, Machine Man, Risque, Siryn, Warpath, Sunspot, Cable, Caliban, Domino, Boom-Boom, Rictor, Cannonball, Shatterstar, Post, Blob, Mystique, Toad, Sledge, Onslaught, Cerebro, Sentinels, Cerebrite Alpha, Cerebrite Beta, Cerebro Prime, Cerebrite, Nina, Jester, Knave of Hearts, Red Queen, Tweedledope, Hulk, Valerie Cooper, Thunderbolts, Moira MacTaggert, Cloak, Dagger, Emma Frost, Weapon Omega (Michael Pointer), Namor, Norman Osborn, Daken, Dark Beast, Meld, Lorelei Travis, Avalanche, Match, Adam X, Hellion, Ares, Captain Marvel (Noh-Varr), Hawkeye (Lester), Ms. Marvel (Karla Sofen), Sentry, Spider-Man (Mac Gargan), and many more.