Harry Dresden didn't catch any detail of his appearance, but describes him as having a "lot of muscle and a ridge of leathery plates running down his spine". Urumviel's coin was among the eleven coins stolen by Thorned Namshiel at Demonreach and presumably given to Tessa.(reference needed)
In Small Favor, Dresden deflected Urumviel by spell into an energy beam as it was descend via rope from the roof at the Shedd Aquarium. Harry saw a flash of is human skeleton when it lit up in the beam. His body landed one of the dolphin pools.
A few minutes later, Dresden noticed that Polonius Lartessa had retrieved his coin from the tank that Urumviel had fallen into. She wonders out loud to Deirdre whether he died of his own idiocy or if the wizard managed to get into the Oceanarium before the sign went up.