Once one of Marvel’s more obscure villains, Dormammu’s popularity has risen in recent years thanks to appearances in various media, most recently in the film Doctor Strange. That being said, it’s a shame that the God tyrant of the Dark Dimension isn’t more of a household name because he’s easily one of the coolest looking villains in the Marvel universe. Fortunately, Dormammu also has the abilities to backup his badass appearance, as he’s easily one of the biggest threats in the Marvel Universe, to the point where he outclasses even Thanos.
Dubbed his “most terrible foe” by Doctor Strange, Dormamu can manipulate mystical energy in order to achieve nearly any effect he desires. His abilities include energy projection, matter manipulation, possession, necromancy, teleportation, and creating demon lords, which could very well be the coolest-sounding power on this entire list. He’s even more of a threat in the Dark Dimension, but as you might expect, he is vulnerable in environments that cannot fuel his flames effectively. We’d say that’s a small price to pay for being a literal fire demon.
http://marvel.wikia.com/wiki/Dormammu_(Earth-616) Source: Marvel Wikia
Turns out fusion isn’t a concept you’ll only see in Dragonball Z! First introduced during the mid-90s in Scott Lobdell and Mark Waid’s X-Men vol. 2, #53, Onslaught is a sentient psionic entity created from the consciousness of Professor X and Magneto. Essentially, Onslaught is comprised of the darkest parts of both characters, as the worst aspects of Magneto’s mind escaped into Xavier’s subconscious following a psychic attack from Xavier that rendered Magneto catatonic. Thus, Onslaught was produced – a garish-looking, muscular beast that, at the height of its power, possessed the abilities of not only Professor X and Magneto, but Franklin Richards and Nate Grey as well.
In terms of classification, Onslaught is well beyond an Omega Level mutant, able to have full mental control over anyone, go toe-to-toe with the Hulk in a physical fight even after the Hulk was “maxed out” by Jean Grey shutting down Bruce Banner’s subconscious influence, and just generally being impervious to any attack thrown his way. It took the combined efforts of the Avengers, X-Men, and Fantastic Four to defeat Onslaught but looked at in a more jaded light, the character was really just used as an excuse for Marvel to launch its “Heroes Reborn” line in 1996.