Grimstone has a vaguely humanoid body, with rock-coloured skin. He has a large triangle-like head with two green eyes. His body is covered in small holes. His hands have three fingers, and his feet have three toes. He also has a small tail, and the Omnitrix symbol is on his stomach.
Powers and Abilities
The only power that Ben has discovered so far is this alien's ability to absorb life force- specifically mana. He likened this to breathing in naturally.
Grimstone has demonstrated no weaknesses so far, save for Ben's hesitation to use him as shown in In The Shadow Of Vilgax.