Harlequin

Harlequin was the ruler of the Unseelie Court of the Fey Wild. Usually taking the shape of a mad jester with a smiling porcelain mask, he was feared in the Fey Wild for his madness and cruelty. Most of his plans involved tormenting Oberon in some way, or ruining his plans, and they ranged from childish pranks to great acts of evil. In addition to ruling over Hags, Darklings, and evil fairies, Harlequin had influence over the mortal world as well, through a criminal organization known as The Snaking Vine, who made pacts with him for Fey powers.
Harlequin's true nature was literally Oberon's shadow. Under his jester costumes and mask he was nothing more than a shadow given shape, and his body could twist into many terrifying forms. He was the second being to ever exist in the Fey Wild, appearing shortly after Oberon did himself, and was given life and personality when Oberon noticed his own shadow, and thought of it as a friend. Together, they made the Fey Wild out of the emotions, dreams, and memories of mortals that give the Plane substance, with Oberon usually making beautiful things out of positive feelings, and Harlequin turning negative ones into "funny" shapes and creatures, often parodies of darker impulses. In this way, Harlequin was like an imaginary friend Oberon created to cope with the emotions he was afraid of.
Eventually, though, Oberon grew prideful of the beautiful things he created, thinking himself a lord or god of the dimension he'd shaped. He became bored and annoyed by the nasty things his shadow created, and eventually tore his own shadow off, and sent him away, rejecting the negative emotions entirely. Harlequin clung to them and, alone, went insane, deciding that all tragedy and mortal impulses were 'funny', and seeking frequent revenge on Oberon for the slight.
Harlequin was a frequent villain for Raina, Opal, and Ira. He was in charge of the Hags: Granny Twigmouth, Auntie Greenteeth, and Mother Gristlegums. He also drove Fir made with the mask and pact he'd offered her, causing her to kill her closest friend, Milla. Using her, as well as a form of Simulacrum made of mud that Fir invented, tried to take the Cloak of Stars from them by force. Finally, he attempted to use one of the Grails to merge the mortal world with the Dark Fey Wild, but his attempt was thwarted by the heroes, with the use of the Sword of Luck. Finally, he was killed in his realm by them.
Campaign 1 Epilogue Notes: Harlequin was killed for good by the heroes, Raina, Opal, and Ira. This caused the death of Oberon as well, and the rise of Queen Tatiana (though short-lived).