For 15 years, Supernatural found its way into the hearts and minds of a legion of fans. And while Sam and Dean's story has concluded, the story of their parents continues with the new series, The Winchesters.
Throughout the original series, Dean Winchester not every decision Dean Winchester made was a smart one. Even though he often doesn't always think his decisions through, there are a number of times when the decisions he made were actually great.
Becoming Death For A Day
"Appointment in Samarra"
For Death to return Sam's soul to his body, Dean must take his ring and take up the mantle of Death for a day, a task that soon proves harder than Dean realizes.
The whole thing turned out to be rigged from the start, with Death intending to teach Dean a lesson about the natural order of things, something that both he and Sam have broken many times before and will break again many times after. Still, the choice Dean made to become Death had to be done to save Sam from being a soulless monster for the rest of his life and so he would learn that breaking the natural order of the world has serious consequences.
Leaving A Message In The Past For Sam To Find
"Time After Time"
After an encounter with the pagan god Chronos, Dean ends up in 1944, potentially stuck there forever due to Chronos not being willing to help him get back to the present. However, he comes up with a clever idea to save himself.
Dean is able to leave a message for Sam to find in the present, trusting that his brother has also figured out how to bring him and Chronos back. His decision turned out to be the right one, and the brothers are able to kill the villain thanks to his absurd weakness: a blood soaked olive branch. Had Dean not made this decision, he would've been stuck in the past, as there would've been no way for Sam to find him and bring him back.
Killing Hitler
"The One You've Been Waiting For"
In what should be one of Dean's best episodes, the Winchesters fight against the Thule Society and their plans to resurrect Hitler. It is in this episode where Dean makes one the best (and easiest) decisions in his life.
The Thule are successful in resurrecting Hitler, but their success doesn't last long as the Winchesters manage to free themselves and kill all the remaining Thule. Dean himself corners Hitler and kills him, ending any potential threat he would've had to both the brothers and the world. Had Hitler escaped the fight, he would not doubt have rallied the remaining Thule in and become quite a problem for the Winchesters. Dean's actions eliminated him as a threat for good, an accomplishment he continues to brag about in the following episode.
Ingesting Phoenix Ashes
"Mommy Dearest"
Eve, the mother of all monsters, served as the secondary antagonist of Supernatural's sixth season. With her powers of creating monsters all by herself, she was a major threat for the Winchesters to fight.
The only way to kill Eve was with Phoenix ashes.
Unfortunately, Eve didn't give them a chance to shoot her with them. Dean, showing another genius moment, drank a shot of the ashes and tricked Eve into biting him, leading to her death. He had no idea that this would work and was taking a risky gamble into letting Even bite him. However, his gamble paid off, and the Winchesters had eliminated another insanely powerful foe from the board.
Keeping A "Friendly" Relationship With Crowley
Multiple episodes
Crowley is easily the Winchesters' longest recurring villain, but in his later appearances, he becomes a somewhat reluctant ally/friend of the brothers, particularly Dean.
Crowley has both helped and hurt the Winchesters multiple times, but it was only after Dean was turned into a demon that he and Crowley really started their friendly relationship. And this friendship would become invaluable, as Dean needs Crowley's help to pull off some of the Winchesters' greatest feats. It's hard to imagine where the brothers would be if Dean hadn't kept his friendship with Crowley, especially with how much the demon helps them out up until his final sacrifice to trap Lucifer in Apocalypse World.