With steel-hard bark, these corrupted beings were once protectors of the forest.
The Tainted Treant is a tough foe that can fight blow for blow with the strongest units. It is slow and only takes one life, so it is not especially dangerous on its own, but they can easily let a horde through whilst they engage your warriors.
Multiple treants will randomly spring up from the ground in the Rotten Forest stage during the campaign. These particularly annoying treants do not provide any bounty whatsoever... Liberal use of magic towers is reccomended to handle these nasty enemies. You potentially might want an Arcane Wizard with the teleport ability to set back the treants that spawn at random points on the battlefield.You may also want to save up your rain of fire for situations such as hordes of tainted treants.