The Omnicide Coalition is an alliance of races and groups that have banded together to enslave, or failing that, kill, all sentient life in Altbeidon. They are led by the Daemons and are subsequently based on Inferno, although a base exists on each member's homeworld.
The following are the member races of the Omnicide Coalition. There are thirteen, all of whom were major threats in their own right before banding together. They are listed with their home fiction and leaders.
Daemons (Multiverses, Hectocapitus)
Daelkyr (D&D Eberron, various daelkyr lords)
Species 8472 (Star Trek, unknown)
Combine (Half-Life, Advisors)
Flood (Halo, the Gravemind)
Chimera (Resistance, Angels or possibly Pure Chimera)
Sontarans (Doctor Who, General Sontar)
Phaaze/Phazon (Metroid, Phaaze)
Yuuzhan Vong (Star Wars EU, Supreme Overlord Shimrra de jure, Onimi de facto)
Lolth & minions (D&D, Lolth)
Yeerks (Animorphs, Council of Thirteen)
Tyranids (Warhammer 40k, Hive Mind via Norn-Queens)
Ori & worshippers (Stargate SG-1, Ori)
I made this partially because a Korgrath riding a Carnifex is the coolest thing ever.