Uses his AC as a billboard where sponsors can place their ads. He's milking his time in the Arena for all he can get. Even so, he's still a very capable pilot.
Billboard is a middleweight two-legged AC equipped with a vertical missile launcher, a pulse cannon, a rifle, a laser blade and an overboost core. In order to use the pulse cannon the unit needs to kneel.
Grenstone is not one of the most difficult ACs but he does tend to stay in the air for a lot of the fight. That means that in an Arena like ithe Caves, he becomes a bit more managable. He also has a good deal of armor that makes him fairly durable when it comes to combat. While he doesn't deal that much damage, his proficiency for staying in the air, so you need to track him. However he isn't that dangerous.