He is one of Ben's aliens when the Omnitrixes are stuck in Nightmare Mode! He is body is brown, black and orange. He now has a horn, new legs, tail, and wings.
- Nightmare Humongosaur can fly.
- He can stab enemies with his poisonous stinger and generate gust of wind with his wings.
- He can ram at enemies with his bone horn, and has superhuman strength and the ability to grow to 70 ft.
- His thick skin grants him durability and protection from minor injuries.