Anti-Hero: Gradually morphs into this by the end of the movie. He's certainly not a hero in the traditional sense, and most of the problems he's faced with were his creations in the first place, but he does save the day.
Anti-Villain: It quickly becomes apparent that for all his grand evil schemes (most of which go for style over substance), he's not truly playing to win. He's baffled that he actually manages to kill Metroman and it doesn't take long before he realizes that he needs someone to step up and challenge him.
Camp Straight: Megamind has Ho Yay, Foe Yay or both with pretty much every guy in the movie, and yet he never gets explicit about any of them in that way (Dreamworks kids' movie, remember?) and actually ends up with Roxanne by the end of the movie following a naturally progressing relationship (so no Last Minute Hook Up there).
Captain Ersatz: Megamind is a mixture of Brainiac and Lex Luthor (with Superman's origin), and by the end of Button of Doom has developed Batman-like characteristics.
Evil Genius: He styles himself as this, and embraces most of the villainous clichés associated with it, including the evil lair, the over-the-top torture devices, the army of robots, and a myriad of weapons and inventions.
Friendless Background: He grew up constantly ostracized and was very much the odd man out at school, due more to his appearance (At least at first) than an apparent knack for villainy.
Freudian Excuse: He becomes a villain because he grew up in a prison and was rejected by his peers for his odd appearance and strange inventions. Anytime he did anything "wrong", Metro Man put him in the corner and he was rewarded for punishing him.
From Nobody to Nightmare: Megamind was actually a sweet kid, but the constant rejection from his peers made him believe that he was "supposed to be bad". Skip twenty years later, and he's the Big Bad.
Gadgeteer Genius: He built an escape trike out of license plates and a binky. When he was a toddler.
Glamour Failure: His holo-watch allows him to look like anyone it scans beforehand. However, he, apparently, forgot to waterproof it. It also shuts off if he bumps it by accident.
Graceful Loser: He takes every failure as a learning experience, no matter how far-fetched his victory may be.
Green Eyes: He has very bright emerald eyes. They remain visible when he morphs into someone else, which is a visual cue for observant audience members.
Hidden Depths: Megamind's confrontation with Hal after he does a Face-Heel Turn shows that the supposed Big Bad who loves getting in trouble actually is disgusted with people who have the potential to be good, don't take it.
I Just Want to Be Loved: Naturally, anyone ostracized by society at large nearly their entire lives would be pretty affection-starved. Especially evident when Roxanne first hugs him. See Post Hug Catatonia below.
Longer-Than-Life Sentence: Got 88 consecutive life sentences for his crimes against humanity and Metro City. Largely meaningless, since he's able to waltz out the front door of his Cardboard Prison, and back into his functional supervillain laboratory lair.
The Atoner: Metro Man seems to regret how much of a jerk he was to Megamind when they were children, and as evidenced by his faith that Megamind was meant to be a hero, understands that he had a hand in making Megamind originally see himself as a villain.
Broken Ace: Despite being the beloved hero and his amazing superpowers, he realized that he was pushed into the role of hero like Megamind was to being a villain. Using his superspeed, he goes to clear his mind, end up reading some self-help books and faked his death so he could retire.
The Cape: Wears an actual cape and is the good guy.
Disappeared Dad: In a weird reversal, Metro Man's parents are hinted to be very uninterested (his father doesn't even look up from his newspaper when he's flying as a baby), while Megamind's "parents" (the prison inmates) treat him warmly like family, despite teaching him Family Unfriendly Aesops.
Genius Bruiser: Played with. In the Prequel comic, Megamind makes their rivalry out as Brains vs. Brawn. Yet his flashback shows that he's not the Dumb Muscle Megamind indicated he was; but even so, his scenes as Music Man seem to hint that he can still be bit of a ditz.
Heroic Build: Is a superhero with a ridiculously buff physique.
Heroic Fatigue: A variation. He wasn't sick of helping people, but felt like he never had a true choice in the matter and decided to retire by faking his death.
Human Alien: Like Megamind, he's also from a far away planet. Unlike Megamind, aside from the ridiculously buff physique, he looks pretty much human.
Jerk with a Heart of Gold: A Smug Super who use to bully Megamind before really getting to know him. However, he does care for the citizens of Metro City and is genuinely proud of Megamind becoming Metro City's new defender.
Just Friends: The press assumed he was sweet on Roxanne, but he's not her type.
Kryptonite Factor: According to himself, his weakness is copper. Turns out, he was lying. What his real weakness is, if he has any, is anyone's guess.
He does have dandruff... but that's probably not a "Weakness," per se. Except that it does allow supervillains to create equally-powerful power clones of him, which would probably be pretty dangerous if said supervillain wanted to create an evil version of him instead of another good one. Unfortunately, the clone wound up turning evil anyway.
Ascended Fanboy: Deconstructed. As a regular human he secretly despises Metro Man because he thinks Roxanne is in love with him. When he gets superpowers he abuses them trying to impress Roxanne and, when rejected, goes on a selfish, childish rampage.
Ax-Crazy: Whenever he gets angry—special note goes to when he discovers Megamind's deception.
Even Evil Has Standards: One of the things he cites as a reason to beat Megamind when attacking Megamind after finding out that 'Space Dad' was Megamind in disguise is that Megamind lied to Space Stepmom, so Hal can consider the feelings of others, sometimes. It also shows that Hal isn't the smartest, but that's not really news at that point.
Evil Is Petty: Turned all evil just because Roxanne wouldn't return his feelings.
Evil Redhead: He has red hair. He becomes evil after gaining superpowers.
Silly Rabbit, Idealism Is for Kids!: Roxanne tries talking some sense into Titan, saying that she knows there's still good in him. He simply scoffs at her that she sees good in everyone, even when it's not there.
Spell My Name with an "S": Most people still aren't entirely sure if his name is officially spelt Titan or Tighten. While it seems that Megamind originally wanted to spell it as Titan, official printed media such as the "Art of" book, the character poster and the closing credits spell his name as Tighten.
Dragon-in-Chief: Minion is arguably a more competent villain than his boss. He often counsels pragmatism (why are we making another hero to fight us again? Can't we just enjoy the good life?) but is constantly overrode by Megamind's approach to villainy.
Minion with an F in Evil: He's so pleasant throughout the entire film, that it's highly likely that he went along with Megamind's evil plans less because of being evil and more because it seemed to make his master/friend happy.
Morality Pet: Played with. He's much nicer, friendlier, and more helpful than Megamind, but in his devotion Minion not only does nothing to stop him from being a villain, he becomes upset when Megamind suggests that they not be evil anymore.
Yes-Man: As described by the filmmakers: "He might suggest that jumping off a building isn't the best idea, but in the end, he wouldn't stop (Megamind); he would just race to the bottom and build a net."