Dark Dimp

Dark Dimp is a Pokemon from Pokémon Rose and Violet Versions, specifically Violet, since he is that version's mascot. He is not known to evolve into or from any Pokemon, but he has several similarities with Dimp. He is a legendary Pokemon.

In the Anime
Dark Dimp, alongside Dimp, appears in the Rose & Violet anime.

Pokemon Legends
Dark Dimp and Dimp are mentioned by Professor Maple while telling Ash, Jonathan, and Olivia about the Bunseed they caught. He

They are mentioned more throughout the series in a similar way.

The Perfect World
The two finally appear in this episode. After Ash, Jonathan, and Olivia get into an argument and split up, Ash finds a group of Bunseeds, Bunsplashes, Bunchars, and Bunzaps, which suddenly vanish. Ash walks over to where they vanished and is teleported into Dimp and Dark Dimp's universe. Frightened, Dark Dimp uses Shadow Ball and attacks Ash, though his Bunseed protects him. Bunseed, Dimp, and Dark Dimp have a short conversation, and at the end Dark Dimp and Dimp welcome Ash with a nearly suffocating hug. Confused, Ash asks them if they can show him where he is, and the two give him a tour.

Unfortunately, outside, Team Rocket watched Ash vanished and decided to check it out themselves. Team Rocket are also teleported into the universe, and after Dark Dimp returns from giving Ash a tour, he watches Team Rocket take all of his servants captive, and blames Ash for letting them in and begins to attack him again. Dimp, however, is a bit more forgiving, and attempts to keep Dark Dimp from attacking Ash, but ends up being hit himself. This causes a fight, reminding Ash, Pikachu, and Team Rocket of the legend. Though Ash, Pikachu, and Bunseed attempt to stop them, Team Rocket manages to capture Dark Dimp and Dimp and escape.

After convincing Jonathan and Olivia that he saw Dimp and Dark Dimp, Ash and his friends follow Team Rocket to their lair underground. They first release the Bunseeds, Bunsplashes, Bunchars, and Bunzaps, which then distract Jessie, James, and Meowth so that Ash, Jonathan, and Olivia can save Dimp and Dark Dimp. Dimp and Dark Dimp team up and both fire a stream of Shadow Balls, knocking Team Rocket into the sky. Dark Dimp and Dimp then allow themselves to be caught by Jonathan and Olivia, and appear off and on assisting them in battle.

PKRV093
They appear again. Their exact role is unknown.