We also had a Muscle character based off of the Cravers from Endless Space. We ran them as being created by the Ur long ago and then left to their own warlike devices.

0 Stress: Four arms that work independently. Sense infared light.

1 Stress: Use your enhanced muscles to lift a thug one-handed. Hear a conversation across the room. Track a creature by the scent of its blood.

2 Stress: Ripping chains apart through sheer strength.