He transformed, likely as a result of excitement combined with his new demonic powers. If you compare how he looks now to a couple pages ago, his primary color scheme is inverted (his main body color is now dark red while his markings are lighter), his horns are substantially longer, his tail is longer, skinnier, and ends in a fuzzy spade, and his outfit is kinkier.
The differences are fairly subtle without looking closely at him here and comparing it to a page where you get a good look at his full body. It's easy to not get exactly what happened.
He transformed, likely as a result of excitement combined with his new demonic powers. If you compar
