Cynicism Catalyst: His only friends spent a short time with him before dying, and then his memories had to be wiped in order to keep the emotional anguish from overloading him during his early stages in the test tube. This left him with only vague flickers of what he remembered with Ambertwo and the other three clones - a sense of grief and loss, accompanied by not understanding exactly why "life is wonderful", or what his purpose is.
Dan Green: He ended up voicing Mewtwo in Mewtwo Returns, due to Phillip Bartlett's death in 2001.
Dark and Troubled Past: The Kanto starter clones and Ambertwo were his childhood friends, but all of them died and the scientists were forced to erase his memories of them to keep his brain waves from going out of control. But even then, he still remembers Ambertwo's last words.
Go Mad from the Revelation: When he finds out the humans who made him don't give jack squat about him. It's traumatic enough as it is, but his childhood friend Ambertwo's last words of "Life is wonderful" are still in his head when he breaks out of his test tube. It's enough to send Mewtwo into a rage and leads him to want vengeance on all non-clone life.
Humans Are The Real Monsters: How he views humans after his early exposure to them. By the end of Mewtwo Returns, he's softened his view on them a bit.
Island Base: Has one in the first film that would make even a James Bond villain green with envy. Its complete with a battle arena, cloning machine and Weather Control Machine (in this case, he's the machine), and all this is on the island where he was created, even including the last log of the scientists he killed months before, as a testament to his birth.
Straw Nihilist: Starts out like this in the first film, but grows out of it by the end.
Super Soldier: Giovanni attempted to make Mewtwo into this in both the first film and Mewtwo Returns. Both attempts end in failure, the second of which resulting in Mewtwo erasing all traces of himself from Giovanni's memory.
Take Over the World: The English dub more or less Bowdlerizes his main goal from wanting to prove himself to Mew that he is the "true one" of the two to simply this.
Used To Be A Sweet Pokémon: The cover for The Birth of Mewtwo radio drama shows him as a happy, little baby Pokémon and has moments where you just want to give him a hug. When Mewtwo grows up and has a better understanding of the circumstances of his birth, he quickly goes off the deep end.
When He Smiles: Twice in Mewtwo Returns; once while moon gazing with Pikatwo and Meowthtwo and again during his healing at the lake, when he finally realizes that the Earth is as much his home as any naturally created Pokémon.
Woobie, Destroyer of Worlds: Both in the English and Japanese version of the first film, though much more in the latter (see Take Over The World above).
Let's Get Dangerous: He spends the first half of the film before confronting Mewtwo bouncing around the island playing. When Mewtwo delivers his Badass Boast that he is superior, Mew just chases its tail, and giggles as it dodges Mewtwo's attacks. But when one of Mewtwo's attacks finally hits and sends him flying through the air? He returns the favor.
Urban Legendof Zelda: Contrary to a popular myth, Mew doesn't outright antagonize Mewtwo in the original version. At one point, Mew claims that the real Pokémon won't lose to their copies, as long as they try their best. That was as far as it ever went, and Mew didn't really consider the clones as inferior.
Pokémon the Movie 2000 - The Power of One
Affably Evil: He doesn't even keep his prisoners locked up, he lets them walk around as they please!
Anti-Villain: One of the most sympathetic in the entire franchise.
Be Careful What You Wish For: Double-subverted. The Unown make a happy, perfect world for her complete with replacements of her missing mom and dad, but eventually their powers get out of control and it breaks down.
But subverted again when they granted her a wish of having a father figure in her life, Entei, who is all about protecting her.
Break the Cutie: She's five, yet she undergoes crap no child that age should have to endure.
Badass: The only one of Ash's Pokémon that gives him even a little trouble is Charizard - who is established to be one of the toughest before getting his training - and even then Entei comes out on top.
A magician who has his show in the Millenium Comet festival. He was once a scientist working for Team Magma on a machine to resurrect Groudon. After his failure, he was expelled from the team, driving him to seek vengeance and prove his theories.
From a Certain Point of View: Aaron sort of brought Lucario's spite upon himself - he might have done what he did to protect his partner from dying with him, but even so he could've arranged for Lucario to learn the truth instead of leaving him sealed in the staff for centuries.
Rescue Romance: Averted - she believed that Tonio had saved her when they were children, but although she probably formed her initial attraction towards him over it, she's still clearly in love with him at the end of the movie. Played straight when Tonio saves her from falling off a bridge.
Butt Monkey: A little, though he's far from cowardly and proves himself by the end.
Jerk with a Heart of Gold: Granted, he's less of a "jerk" and simply seems a little more inclined towards aggression than negotiation, which can't have helped the public opinion of him. Despite this, there's a major emphasis on his Heart of Gold.
Ambiguous Gender: Its mannerisms shift whenever its forms do: in Land Forme, it behaves like a meek little girl, and prefers being with Dawn; in Sky Forme, it's more akin to a headstrong young boy, and bonds better with Ash. Even its voice changes between the two forms!
Disney Villain Death: An interesting variation in that he isn't a villain, but because of how he originally died he was believed to be one for millenia. When he survives due to changing the timeline, he's rightfully regarded as the noble man he was.
Well-Intentioned Extremist: He firmly believes that Michina Town will die once the Jewel of Life is returned to Arceus, and so takes measures to ensure this won't happen. Subverted in the manga adaptation, where he's a lot less sympathetic.
God Is Evil: Well not evil but close at the start of the movie
Hero Antagonist: Its grievances with humanity aren't unjustified even thousands of years later - it was almost murdered by people it had saved with no benefit to itself save the satisfaction of doing good!
Heroic Sacrifice: Almost pulled one to save the land from a meteorite. This is how hit met Damos.
I Owe You My Life: Why it repaid Damos initially, though it appears Arceus was by nature sympathetic to those in need.
Meaningful Name: His Japanese name, and by extension his English one, comes from the Japanese word for "megalomanic".
Obviously Evil: Inverted - his appearance is a little bizarre but not overly suspicious by his own world's standards; however to the audience it fittingly invokes Light Is Not Good with his white suit and gold eyes, because very rarely does a character with both that and Kaleidoscope Hair turn out to be a saint.
Person of Mass Destruction: Twenty years before the events of the movie, he caused all the plant life in Crown City to die by touching the Time Ripple.
Chekhov's Skill: His ability to take on the appearance of another Pokémon comes in handy near the climax of the movie, when he masquerades as Celebi and lures Kodai away to give Ash more time to bring the real Celebi to the Time Ripple.
Dark Is Not Evil: "Adorable little fox kit who just wants to be reunited with his mother" is about as far from evil as you can get.
Action Mom: Trapped in an electrified steel cage? She punches her way out of it. Confronted by a trio of legendary Pokémon? She fights them to a standstill. Facing Grings Kodai himself? Destroys his Time Ripple absorbing claw and knocks out his Shuppet with Dark Pulse. What motivates her to pull this all off? Her son needs her.
Poor Communication Kills: Got in a big fight with Shiny Raikou, Entei and Suicune because she was running around giving them a bad name, even though it wasn't her fault. Can't these movie Pokémon just talk things out?!
Large Ham: More quiet than most hams, but his voice makes any speaking have impact. Then there is the way he accepts invitations to a fight: set up an icy combat ring with an arc for the challenger to pass through as formality.