Picture done by the inestimable  sammysapphire

Cale wasn't aware at first, but his body had an unusual reflex. In response to certain stressors or events, he would transform. This is one of those forms, named by him Obsidian Maximus. He first discovered this form after deciding to get into shape and getting a gym membership. On his first visit, after working out for ten minutes, he found himself swelling with muscle, arms and legs transforming into tree trunks as his chest broadened outwards. His wings grew larger to support his enlarged frame and he started at it in wonderment.

Becoming Obsidian brings about a few changes to Cale's personality. He becomes more aggressive and more horny, although he's still as much of a gentleman as ever, so this form tends to be more chivalrous, eager to jump to the defense of any fair maiden in need.

The triggers for Cale becoming Obsidian are physical distress, such as being threatened or physically in danger, intense arousal or hard physical activity.