These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Awesome Ego: The most gloriously hammy and Shakespearian of all the X-Men villains. Its rare indeed for a story featuring the character to go by without him -rightly- bragging about his awesome power or invincibility, or references to notions like triumph or eternity in relation to himself.
An Ancient Egyptian shapeshifter with a Social Darwinist streak, En Sabah Nur ("The First One"), better known as Apocalypse, is one of the oldest, and one of the most evil, mutants in existence. Believing that the strong must dominate the weak, Apocalypse aims to test humanity. Those who survive the process will be allowed to live as his servants, those who fail, die. Apocalypse has a history of granting powers to other unscrupulous individuals, transforming Nathaniel Essex into the mad geneticist Mister Sinister (in exchange for Sinister agreeing to unleash a plague that would exterminate most of humanity), and empowering terrorist leader Moses Magnum, in exchange for the latter winnowing out the strong from the weak. His other crimes include, infecting the infant Cable with a techno-organic virus, turning Cable's clone, Stryfe, into the monster he is today, trying to force humanity to reduce its own population by 90% or face the wrath of another metaplague, and effectively killing Stryfe by bodyjacking him. That's without getting into the Bad Future, where he rules most of the world and has effectively run it into the ground, or the Age of Apocalypse timeline, where he devastated North America with nuclear weapons, reduced the human population in purges, and gave free reign to likeminded psychopaths Sinister, Holocaust, and Mikhail Rasputin, effectively destroying civilisation. Believing wholeheartedly that those he considers weak must be slain, Apocalypse is well-deserving of his name.
X-Men: He is a would-be mutant conqueror who despises everything that isn't him and fancies himself a God. In his first appearance he builds a machine designed to take away people's free will and make them his slaves. He tricks four self-loathing mutants, including Warren "Angel" Worthington, into believing this machine will cure them of being mutants, preying on their feelings of inadequacy to subject to them to a painful process of transformation them into his Four Horsemen of the Apocalypse. Apocalypse then orders his Horsemen to go on a rampage across the globe. Rogue was able to free Angel from Apocalypse's control with her Power Absorption abilities, but Angel was a mentally unstable wreck after that experience. In his next appearance, Apocalypse creates a plague designed to wipe out most humans and mutants. This plague furthers tensions between humans and mutants, with some humans blaming mutants for it and creates a Bad Future, where several mutants are dying from this plague. Later Apocalypse manages to get hold of some time travel technology and uses it to travel to the Axis of Time, a interdenominational area that controls time itself and plans on destroying the time stream and reality itself, so he can recreate it in his own image.
Magnificent Bastard: He has successfully brainwashed numerous heroes into doing his bidding, including Angel, Wolverine and even the normally uncontrollable Incredible Hulk. He is so smart and powerful and has such advanced technology that he was able to take Loki prisoner, has defeated Dracula in battle (and before that, when Dracula was slain in battle back when he was a mortal, it was Apocalypse who defeated and killed him), and has canonically taken over the planet multiple times in numerous parallel universes. Apocalypse has cheated death on numerous occasions, turned entire nations against themselves and each other, and has received the worship of humans, mutants and even a faction of the alien Skrulls. He has outfought and outwitted aliens, immortals, vampires and gods, defied the time-travelling warlord Kang The Conqueror who had travelled back to ancient Egypt to recruit him in his youth, and once came perilously close to stealing the power of twelve of the most powerful mutants on the planet which would have made him The Omnipotent. He is one of the most rightly hated and rightly dreaded enemies of the X-Men and many other groups of heroes and villains, and he is not remotely intimidated as nobody has ever been able to permanently kill him.