You're learning!
Iguanas are a whole different deal than Bearded Dragons and WDs!
Try taking him and putting him in the tub under a little warm running water before handling. This will cause them to "go" in the tub and there won't be anything left to decorate your shoulder with.
The tail description concerns me. The withered portion of the tail has been damaged and the tissue has died. This is common with iguanas. Often the withered area will fall off on its own. The problem is an affliction known as dry gangrene. The necrotic tissue causes an infection that will progress up the tail and reach the body of the ig killing it. Dealing with dry gangrene is simple if unsettling to us. The diseased portion of the tail will have to be surgically amputated. The vet will most likely also perscribe antibiotics.
Take a permanent marker like a sharpy and mark the uppermost area of the dark part of the tail. If the darkness goes past that mark get the ig to a herp vet immediately.
