I could see Doctor Doom, Kingpin(Spider-Man TAS), and Loki(or Hela) myself. Kingpin could have members of the Sinister Six(Doc Ock, Mysterio, Vulture, etc.) as his allies, similar to the Hyenas or Lock, Jock, and Barrel.
I do not see Thanos's goals, MCU or comics, really aligning with what Maleficent wants. Similar issues with Galactus, who is not really a villain but rather an important part of the universe.
Magneto is not evil and he only wants mutants to prosper by any means necessary. I can't really see him siding with someone who wishes to engulf all the worlds, and by extension all mutants, in darkness.