Darkrai (Explorers of Time, Darkness, and Sky)
Darkrai is the main antagonist of Pokemon Mystery Dungeon 2. Though he mainly appears in the post ending plot, he is revealed in the end to have orchestrated the events of the entire game.
History
Darkrai first appears disguised as Cresselia in the player's dreams, telling them they are causing a distortion in the fabric of space that could plunge the world into darkness and neverending nightmares because they came from the future. When Azurill falls into a nightmare that doesn't end, the team goes to find a reformed Drowzee to send them into the young pokemon's nightmare to find out what's wrong. There they encounter a Cresselia, who tells them the same as the player was told in the dreams and tries to destory them but is interupted by Drowzee.
The partner is discovered to be having simular dreams, Cresselia telling them its because they came back from the future and is deeply upset by it. They decide to go see Palkia, the Pokémon controling Space. However, before they can do so, Palkia arrives in their base and takes them to his lair in spacial Rift, planning to destroy them, believing they are destroying the fabric of space. The two manages to escape Palkia and defeat him, however, Palkia becomes trapped in a nightmare. Cresselia allows them to enter his dreams to discover what's wrong. Cresselia tries to have Palkia destroy them. Palkia questions Cresselia, revealing he'd been told the team was trying to disrupt space. Before Palkia can finish them off, a second Cresselia arrives and exposes the first 'Cresselia' to be Darkrai, who she'd been persueing for a long time. Darkrai escapes but offers them the chance to stop him from disrupting space at Dark Crater.
Cresselia reveals to the team it was Darkrai that was behind the near destruction of Temporal Tower and the dark future the player came from, seeking to make a dark world he could rule as his own. Though the player and their partner do cause a distortion, it is not large enough to be a threat on its own but Darkrai was expanding it. Darkrai's deception was a ruse to try to destroy the team because they stopped his last plan and stood in his way. She is concerned that Darkrai's challenge may be a trap, as he normally flees when confronted but the group decides to trevel to Dark Crater with Cresselia to stop him.
At the bottom of Dark Crater, they challenge Darkrai, who reveals it was him that caused the player's memory loss by attack him and Groyvle in the time stream, the player taking the hit for his friend. Despite this, the team prepares to battle Darkrai but he offers them the chance to join him and rule the world. It appears the partner takes it, having given up all hope. However, when the player realizes how uncharacteristic the partner's actions are, they attack Darkrai, revealing it was a nightmare induced by Darkrai. Darkrai summons a group of Pokémon to assist him in eleminating the group but it proves to be in vain.
Cresselia moves in on the defeated Darkrai to finish him but Darkrai tries to escape through a Dimension Hole. Though he is unsure of where it will take him, Darkrai is confedent he'll be able to complete his plan in another place and time. However, Palkia arrives, tired of Darkrai's threats to the fabric of space and destroys the Dimension Hole right as Darkrai enters it.
Darkrai is not killed but like the player, has his memory erased and is teleported somewhere else in the world. With his thoughts of world domination erased by this, Darkrai is left to waunder the world. He can be encountered in several places after this but his personailty is vastly diffrent and if recruited, will prove to be quite loyal to the player.