Mewtwo

The Pokémon Mewtwo was created in an island laboratory from the DNA of Mew, a rare Pokémon believed to be extinct, recovered from fossilized remains. Displeased with the concept of being nothing more than a mere lab experiment, Mewtwo destroys the laboratory. Shortly afterward, he meets Giovanni, the head of Team Rocket, who proposes a partnership with the Pokémon in exchange of helping it control its powers. Mewtwo is "trained" over the next few months, being pitted against challengers in Giovanni's gym and restraining Pokémon for Team Rocket to capture. Mewtwo eventually realizes that Giovanni is merely using him as a tool and destroys his headquarters. Mewtwo flies back to the island where it was created and begins plotting revenge against humanity.

Meanwhile, Ash Ketchum and his friends Misty, Brock, Pikachu, and all their Pokémon companions receive an invitation to a party hosted by the world's "greatest Pokémon Master" on New Island. Ash and his friends are excited and rush to the docks in an attempt to catch a boat to New Island, but a storm is mysteriously formed and all boat rides to the island are canceled. Undeterred, several trainers make their way out to the island by riding their Pokémon, though neither Ash nor his friends have any Pokémon of their own that can help them safely navigate the stormy sea. In their latest plot to steal rare Pokémon, Team Rocket offers the trio a lift to the island, disguised as a pair of Vikings, but their small wooden boat is destroyed by a wave. Ash and his friends manage to reach the island with their aquatic Pokémon, and are escorted inside the palace on the island.

The trainers are unable to bear this senseless violence, even while the two sides grow fatigued and Mew and Mewtwo continue fighting. In an attempt to put an end to the ordeal, Mew and Mewtwo sum up all their remaining powers for one final duel. As they open fire however, Ash runs to the center of the arena in a brave but desperate attempt to stop the fight. The attacks fatally strike the young trainer, and he collapses in the center for the arena. Pikachu runs to the side of its trainer only for Ash's lifeless body to be turned to stone. After trying to get him off the floor, Pikachu attempts again using thunderbolt, but in vain. In its grief, Pikachu starts weeping for its fallen master, the other Pokémon in the arena doing the same. The tears reach Ash, their mystical healing powers reviving him. As everyone rejoices, Mewtwo, taken aback by Ash's act of selflessness to save all the Pokémon, has an epiphany over the relationship between humans and Pokémon, and realizes that the circumstances of how one is born should not be allowed to divide anyone. It leaves the island with Mew and the cloned Pokémon, erasing everyone else's memory of the horrifying incident, knowing it's for the best.

Ash and his friends find themselves back on the docks with no idea how they got there. Ash looks up to the sky and spots Mew flying past, and recounts to his friends how he saw the rare Pokémon Ho-oh on the first day of his journey.  Got from wiki.