Perhaps, but to even use them you need the Legacy of the Ancients DLC, which also introduces umbra type enemies.
Pretty sure the umbra is from corrupted skies or tainted horizons or something. It's a later dlc for sure. Legacy just adds the super weapons, excavation maps and the mechanical enemies you find there.
Yeah! It's not as massive as a rework as I expected, but it was good. I made a fairly lengthy post about it a few pages back.
No, Legacy of the Ancients adds the Umbra. The Umbra is literally the result of Pandorans being exposed to one of those special resources it introduces. Legacy also introduces crystal type enemies that deal more damage the more you hurt them and a type of Siren that has even more armour (orichalcum siren or something)
I'm playing Corrupted Horizons and Infested Skies right now without Legacy of the Ancients and they do not appear, and the game is so much better for it.
Umbras are a cool concept and I understand that they are meant to be a Chrysallid analogue, but they are so incredibly inconsistent and cheap.
I've seen them die as soon as they walk through fire, I've seen them wade through fire as if it was nothing.
I've seen them not spawn when a pandoran dies to fire damage, I've seen the pool form in a lake of fire.
It doesn't help that the wiki tells you that if the host dies to fire it will not spawn, which apparently is only true sometimes but completely false other times.
It doesn't help that they spawn right after you kill the enemy on the enemy turn will full AP, meaning that with their high movement points they can run up to a soldier and instant kill him with up to 3 90 damage 20 piercing attacks. Even if you war cry it it can still potentially make the distance and cripple a limb.
It doesn't help that the bastards spawn everywhere. Lids at least would only spawn on terror missions and enemy bases. Umbras can be found anywhere, even in nests where is worse possible place to fight them due to close quarters. Nests with Legacy active are actually harder than lairs or citadels for this reason.
It's just a poorly designed and buggy enemy type that is more frustrating than challenging. Smaragdus Chirons and Scyllas encourage you to go for big hits instead of a lot of small ones to counter it's damage buff. Siren Armis encourages you to take a lot of acid and shredding weapons. Umbras encourage you to save scum in case the fucker decides to spawn in a lake of fire.
Gollop should have continued working on the game to refine it instead of releasing it early on Epic like a greedy bugger, and fucking over his kickstarter base in the process.