Summons a Bone Colossus for 60 seconds. While active, conjured skeletons regenerate health and you can summon 2 additional skeletons. Only 1 colossus can be summoned at a time.
Allied skeletons and draugr heal 3 health per second if they are within 1000 range of the Colossus.
Conjure Bone Colossus will despawn all other summons upon being conjured regardless if you have the Twin Souls perk or not.
If you have the Twin Souls perk, the next summon you conjure after Bone Colossus will take up the Twin Souls slot. So for example casting Conjure Bone Colossus, 2 Conjure Skeleton Champions, and a Conjure Dremora Lord will result in the Bone Colossus and one Skeleton Champion being despawned.
If you conjure a summon that qualifies as a extra summon after you've used up all your summon slots then the Bonecolossus will be despawned without despawning the other extra summons. So for example casting Conjure Bone Colossus, Conjure Dremora Lord, and 3 Conjure Skeleton Champions will result in an army of 1 Dremora Lord and 3 Skeleton Champions.