Cultists will need to give their mortality to summon these Super Units, which are limited to one per Underlord. Which one you can lure depends on Wrath, Sloth or Greed.
Three Veins can be pursued by Underlords which unlock certain bonuses and minions for use, which includes which Super Unit will be tempted for a visit.
"You’ll be able to acquire these super units by unlocking the relevant ritual at the very end of your chosen Vein, then performing it by sacrificing a max-level Cultist in your Sanctuary (a room we will be revealing this month). Additionally, you’ll only be able to command a single super unit at any one time," Subterranean.
The Behemoth (Wrath), the Eternal (Sloth) and the Archon (Greed) are all detailed.
War for the Overworld remains in beta and is available through.