Here's my work-in-progress Sparky detail paint. Honestly I might just stop while I'm ahead...any other subtle details might not even be noticeable when he's at the back of the playfield.
-Tallica Sux on his shirt.
-White on his pupils so it's the "U" shape of Donny's pupils
-Bloodshot eyes (I went a bit too thick on the veins, but I think it will look fine from the players POV...if I had to do it again I'd probably just use a fine red pen)
-Yellowed up the teeth (subtle)
-I was going to paint purple under his eyes...but it looked weird. When I cleaned it off, it left some purpple in the crease under his eye. Subtle but looks cool.