Friends to Enemies Trope

Community - Troy and Abed during the Pillow and Blankets episodes

Shauna & Jackie in the first season of Yellowjackets

Buffy and Faith - Buffy The Vampire Slayer

The new Guy Ritchie Young Sherlock series is doing it with Sherlock & Moriarty. Only S1 so far, but like Smallville it's just a matter of time since these well-defined characters have to get to an adversarial end point (assuming the show gets picked up).

Adora and Catra on She-Ra. Best FtE ever.

Maybe Ted Lasso and Nate?

Adora & Catra, She-ra Orion Pax & D16, aka Optimus Prime & Megatron, several series but most notably Transformers One.

The entirety of Cobra Kai is LaRusso and Johnny butting heads then working together, then butting heads then working together

It’s got to be Flint and Silver in Black Sails

Walter White and Jesse Pinkman

She-Ran and the Princesses of Power, which is nl longer streaming anywhere in the US (AFAIK, but there are _alternatives_)

Justified

There was an episode of Poirot where it turned out that this was part of the solution - it was called "Wasp's Nest" and the episode revolves around Poirot meeting a close association and realising the young man's life was in danger so Poirot had to prevent a murder. But here's the twist - >!the young man was the "killer" of the episode. He found out his girlfriend was cheating on him with his best friend and, finding out that he was terminally ill, decided to kill himself with cyanide that said friend had bought (with his name on a register) to kill some wasps on the culprit's property, the idea that he'd not suffer a deliberating and slow death while also getting revenge. Poirot ended up figuring out the scheme and swapping the cyanide with soap crystals.!<

Leo and Karai- Ninja Turtles

Upvoted just for the 12 Monkeys shout-out. Kirk Acevado is so good.

Aang and Zuko, even though it was set up that way from the start, it's still fun to watch

Kalinda in general was such a better person than Alicia, the show did her dirty by trying to make her the bad guy. the "enemies" drama with them felt like an afterthought from lazy writers. Dawson was insecure and jealous because Pacey will always be the better choice. (R.I.P. James)

The Doctor and The Master were friends as kids on Gallifrey

Optimus and Megatron in recent continuities. This is a trope I really hate, especially with Transformers. I see no reason they should ever have even known each other prior to becoming faction leaders.

Firefly - Allosaurus' betrayal of Stegosaurus was so sudden, and yet inevitable.

Mr. Krabs and Plankton -Spongebob Squarepants Watch the episode Friend or Foe. They grew up together and technically made the secret formula together, and had a falling out. Friend or Foe is technically non-canonical now, but they are still friends in Kamp Koral. And that takes place before the main series.

Wasn't the whole thing on DC simply due to the actors not getting along?

Goku and piccolo