Omega

Being thrown into an anti-matter universe
In the Dark Times, Omega was working with Rassilon to make time travel. Omega ended up inside a black hole which thrust him into an anti-matter universe

Fight with the 14th and 15th Doctors
Omega found a way to take things from other universes and put them in ours. He used that to get himself out of the anti-matter universe so he could find all the incarnations of the Doctor and torture them enough so they would tell him how to find Gallifrey. The 14th Doctor escaped and the 15th Doctor was never captured. Together, they used their TARDISes to pull Omega back to the anti-matter universe, but he still wreaked havoc, sending creatures from other universes, like the Cybus Cybermen and Dragons.

Eventually, he was destroyed along with the anti-matter universe by the Time Lords.