The trickster

The Trickster is deity breaks the rules of the gods or nature, sometimes maliciously but usually, albeit unintentionally, with ultimately positive effects. Often, the rule-breaking takes the form of tricks or thievery. Tricksters can be cunning or foolish or both; they are often funny even when considered sacred or performing important cultural tasks. He plays a unique role in the show, in that he's not entirely against or with the Winchester brothers. Although he plays an antagonistic role in both of his appearances, he does not kill either of the hunters when given the chance, and even attempts to teach Sam a valuable lesson. He even goes as far as turning back time so that Dean's death can be reversed, but only after warning Sam that he would have to learn how to let his brother go. Nonetheless, his morbid sense of humor isn't shared by the brothers, and his playful pranks usually end up being brutally violent or completely fatal. Hence why he is their target to be slain in both the episodes he appears in.

Season 2
He makes his first appearance in the episode Tall Tales as the Trickster, where he is the source of several violent urban legends coming to life and punishing those residing there. Sam and Dean investigate and eventually figure out his identity. However, the trickster is waiting for them, and offers them a peaceful resolution so long as they let him leave to terrorize another town. Naturally, the Winchesters refuse and attack him, along with the help of Bobby. After fighting with various familiars conjured by the trickster, Dean manages to stab the trickster while he is distracted, causing his creations to disappear and the fight to end. However, the trickster that was killed was actually a copy meant to replace him during the fight

Season 3
Later reappears in Mystery Spot.He traps Sam in a seemingly infinite time loop, where Dean continually dies in increasingly strange ways (once by Sam's own hand), with Sam continually failing to save him. After a countless number of repeats, Sam eventually realizes that a trickster must be at work, and manages to locate the culprit. He threatens their tormentor with a blood covered stake, causing the trickster to reveal himself and agree to break the loop. However, when Sam then considers killing him anyways, the trickster restarts the loop. Dean once again dies, but this time there is no loop to revive him. Throughout the next several months, Sam becomes a far colder and more calculated person as he attempts to track down the trickster, killing whatever threat he can along the way. Eventually, it is the trickster who calls the younger Winchester to him, where he tries to drive in a point: that the two brothers continually sacrificing themselves for one another would bring no good, and when people die, they just have to learn to accept it and live with it. Nonetheless, Sam pleads with him to turn back time so that he can save Dean. Reluctantly, the trickster agrees, lamenting that the whole situation had become boring months ago for him anyway.

Season 5
In Changing Channels it is revealed that the trickster is in fact the archangel Gabriel. He traps Sam and Dean in a TV world, so they will say yes to Michael and Lucifer, and the war will finally be over. Sam and Dean manage to trap him and retrieve Castiel, who the trickster had captured. After watching his brothers fight between each other under Michael and Lucifer, Gabriel gave up on God and fled to the earth, hiding in the form of a pagan god. Saying "I skipped out of heaven, had a face transplant, carved out my own corner of the world" He reveals to Dean and Sam that for angels, the Apocalypse has been foretold and unavoidable, with Sam and Dean's role predetermined since Creation. He even compares Sam and Dean's personalities and family life to that of Michael and Lucifer. The trickster hopes to simply end the fighting with the Apocalypse, regardless of who ever wins. Refusing his belief that such things cannot be changed, Sam and Dean leave, but not before Dean frees him from the trap and accuses him of giving up because he is simply too afraid to stand up to his family.

Powers and abilities
He is extremely powerful and he can effortlessly create anything from thin air, even an exact duplicate of himself. He has also displayed a potent degree of time manipulation, being able to trap an entire town in a time loop, and yet singling out only Sam as being completely aware of it. He can also turn back time to seemingly any point he wishes, going so far as to send Sam back several months and preventing Dean's death (for the time being). He has also displayed the ability to disguise himself (although he generally maintains a human image), as well as possessing telekinetic abilities (as seen when he telekinetically retrieves the stake from Sam), and he is effectively immortal. The only thing capable of killing him is a special kind of stake dipped in the blood of his victim, and even then he has managed to escape being killed several times.

Season 2

 * Tall Tales

Season 3

 * Mystery Spot

Season 5

 * Changing Channels