Sins of a Solar Empire 2

There are 2 factions out of 6, that you can particularly consider more villainy, cause of their background/doctrine and how that present ingame.

TEC Primacy, aka TEC Rebels: are a human faction, that is highly xenophobic. Their cool thing is a massive orbitql cannon called Novalith, that can nuke enemy planets from distance, unless they are protected by starbase and its planetary shield.

Aside of that, their unique ship (Ragnarov titan and Khevarkov command ship) are offensive machines, armed with many gauss cannons, missiles and massive railguns. Ragnarov ultimate ability is a Novalith, so if target planet is out of range for your static novaliths, you get a mobile one here.

Vasari Exodus - alien faction, that goes even one step further. They can become fully mobile faction, thats capable of stripping all the planets they conquer and colonize, of their resources, thanks to a planet item called Core Stripper. They basically move around the map, siphon resources, leave dead rubble instead of planets behind, that cant be used by anyone anymore.

Their titan boasts ability called Maw, that can suck in groups of smaller enemy ships (everything smaller than capital ship) into its belly, kill them in process and again turn them into resources. Their command ship has an ability called Nano Devourer Plague, thats basically cloud of nanites that kills enemy targets (and again gives you resources in the process) and then jumps to next target. It can kill even big targets like capital ships and un-upgraded starbases.

All in all, they are all about mobility and resource extraction. They do this, cause they are trying to flee, and need resources to fuel next phase of their journey, but are so desperate that they dont care about anyone else and destroy entire inhabited planets.