Good guys go bad

So if you could write a story or pitch an idea for a heel turn who would it be and how would you have it done?

Dark Obi-Wan, a character set to be in the cancelled Star Wars Battlefornt 3, looked like a fucking radical design. After encountering the ghosts of some Sith ghosts, Obi-Wan's spirit goes to the Sith home world where he is resurrected as a dark lord. He then goes back to Endor where everyone is still partying after Return of the Jedi and has a showdown against Luke Skywalker.

Peter Parker, instead of adhering to his uncles advice, he takes revenge on the thug who killed Uncle Ben.

Then goes on to use his powers as a high level thief, able to enter any place, regardless of security or placement.

This causes him to come under scrutiny from the Thieves Guild, who eventually recruit him, which leads to shenanigans with the X-men.

Captain America Kills the Marvel Universe would be fun.

Venom and Toxin fighting over Eddie Brock would be fun. Then possibly throwing Toxin on Flash Thompson and putting Venom on Eddie.

I think Booster Gold would make an awesome villain in the current DC Universe. Everything is set up for it to work too, since it's been stated that he remembers the old universe.

Re-Introduce him in the Flash. He starts by pleading with him to help him set things right (for added desperation have Booster's version of the DC universe be one where Ted was never killed). But what Booster sees as setting things right, the Flash sees as destroying an entire universe for the sake of one man's, possible delusional, memories (either because Flash doesn't know who Booster is, or, because Flash knows who Booster is and thinks all the Time Travel could have messed up his memories). Have Booster try time and time again to convince Flash, growing increasingly more desperate. Eventually Booster discovers that the only way to bring the old universe back, if the Flash won't help, is to pull him into the time stream and kill him which would cause a "reset".

Booster tries once and nearly succeeds, leading to the Flash going to the rest of the Justice League for help bringing this guy in. So during their second encounter Booster faces off against the full might of the Justice League, which he's unprepared for. After getting his ass thoroughly kicked, Booster manages to escape. This prompts him to become a Justice League villain, and lets him face off with the individual members and the team on various occasions, obviously failing to kill the Justice League members each time.

But after each defeat Booster comes back more prepared, and eventually realizes he needs a team of his own (because Booster is kind of an idiot so it takes him a while to figure things out, and because he's not the most original so he's not above using old cliches) and he begins recruiting heroes and villains who would want the old universe back. This leads to a brand new crises event (because it's DC and they haven't had one of those for a while) where heroes and villains fight over the fate of two different universes. And Booster turns the tide of the war when he discovers the note to Batman (from the end of Flash Point).

Booster has a one on one with Batman, where he shows him the note. Batman reads it and asks, "Would your universe bring back my parents?" and Booster replies, "No. But think of all the parents, the children, the families who would be brought back. Clark's parents would be alive. Roy's daughter would exist..." Booster details everyone who would be brought back and all the reasons for fixing the Universe, and eventually convinces Batman to help him.

During the climatic final battle, Batman turns on the Justice League, allowing Booster to take the Flash into the time stream. Ultimately, they both die in the fight causing three very important things. Booster Gold, the villain of the story, is allowed to die a hero - but no one knows it, making his sacrifice all the more heroic. The new Universe is a merger of the Pre and Post Flashpoints DC, taking the best from both universe and combining them. And finally, Berry Allan is, once again, remembered as a hero who sacrificed himself to save the universe, but this time no one remembers exactly what happened.

Alright, second idea, this time from Marvel. 

Odin and the Asgardians  
After an attack on Asgard that nearly destroyed the entire kingdom, Odin has has enough of Thor protecting Midgard. He confronts Thor, telling him to come home once and for all, and Thor refuses as always. Odin tells Thor that if he wants to stay on Midgard, Thor must defeat him in combat. Odin doesn't hold back, and accidentally kills Thor. 

The All Father grieves for months, and no one can help. Not until Loki manages to find his way to his to his father's side. Loki convinces Odin that, it is not his fault that Thor died, but rather the mortals on Midgard who twisted Thor's allegiance and turned him against his home and his family. They spend hours talking, and Odin finally decides that Midgard must be punished. It's heroes will be punished, it's people made slaves, and - as his remaining son - Loki will be made their king. 

The Warriors Three and Sif try and stop the All Father and Loki, but are no matched. They are not killed, however, they are left broken to serve as an example to all other Asgurdians that might defy the All Father. Meanwhile, Loki works his magic to forge and alliance between the Agardians and the Frost Giants. Together the armies march on Midgurd. 

The Avengers are the first line of defense, but without Thor are over powered. Loki, using magic, reverts Hulk back to Bruce Banner and the Asgardians keep him as a slave. As Banner, they force him to teach them about Midgard technologies, and as the Hulk they unleash him on their enemies. Captain America is killed, Odin takes his shield and wears it into battle. Iron Man, seemingly, retreats. The rest of the Avengers scatter and attempt to gather what resources they have in order to fight back. 

While the Asgardians do battle with other super teams such as the X-Men, the Fantastic Four, and all the other heroes, humanity begins to lose hope. True, some battles are won on behalf of the Earth, the Asgardians hold most victories in the war. Banner, still unwilling servent of Asgard, convinces Loki that he must demonstrait his power over the Earth by "building his kingdom in the heart most powerful nation on the planet". Loki smiles and asks, "You purpose I take over your 'White House'?" To which Bruce responds, "No, I prose you take over Latvaria, and you do it by defeating Doctor Doom yourself." Loki attacks Doctor Doom directly, and manages to take Doom's castle. But Doom escapes, and joins forces with the Earth's heroes. 

The tide of the war begins to even out. Things further favor Midgard when Iron Man returns, leading the Guardians of the Galaxy and Beta Ray Bill (for purposes of this story, Beta Ray isn't with the Asgardians). The tide of the war is turned in the favor of the Earth.

Doctor Strange and Doctor Doom both face off against Loki, while Iron Man and Beta Ray do battle with Odin. Doctors Doom and Strange manage to break Loki's control over The Hulk, which marks the final nail in the coffin, as the magical prowess of Sorcerers and the raw power of the Hulk combine. Meanwhile, Iron Man and Beta Ray are fighting a losing battle against Odin. Iron Man is the first to be taken out of the fight, while Bill and Odin clash. And just before Odin delivers the final blow, Tony reveals that the Guardians and Bill weren't the only ones he met on his trip to space, "I also ran into a little guy known as Galactus. He was pretty hungry, and so I informed his that Asgard was pretty uninhabited at the moment... If you go now you might get there in time to stop him." 

Odin and Galactus has an epic battle over on Asgard. And with the All Father gone, and Loki having fallen, the armies of the Earth manage to defeat the remaining armies of Asgard. Odin defeats Galactus, but only barely. The remaining Avengers, along with Beta Ray Bill, arrive on Asgard and finish Odin off in his weakened state. Now, with Loki, Odin, and Thor all dead, Beta Ray Bill is made the new All Father, carrying both Storm Breaker and Moljnir at his side. Iron Man takes Captain America's shield, and as a monument to the fallen hero, incorporates it as a new chest piece in his armor.