Prethoryn Swarm defeated by... AI federation with ~30k fleet

[Mitchz95]

Okay, the Scourge arrived and, because their starting forces lacked any armies, they had absolutely no way to capture planets. I ended up killing a couple of colonies in their area just to give them a fighting chance. Now they're thriving, much to my gratitude and my empire's lament, but that issue probably never should have happened.

EDIT: They spawned over a moderately-defended AI homeworld so it's possible the armies were killed on the spot. But there should be more armies spread out so they can't be destroyed in one fell swoop.

 

[Drowe]

The Unbidden can be quite challenging, although the only time I've encountered them I was simultaneously fighting in the War in the Heavens as the leader of the League of Unaligned Worlds, that may have had something to do with it. Basically I was fighting 60% of the Galaxy and the Unbidden more or less by myself, because none of the AI Empires did anything against them.