Daisy

Daisy is the most horrifyingly powerful of all Orkish contraptions, who has a special affinity for running over explosive barrels, and shrugging them off as if nothing happened.

Specifically, Daisy is a Battlewagon, and an optional boss in the campaign of Dawn of War II: Retribution. I suggest you bring along a lot of anti-vehicle weaponry. Not that it'll help, Daisy has 99% damage resistance against everything until it's hit all three explosive barrel clusters.