American Toad weird symptoms. New owner, need help

[KP]

This all sounds like a typical shedding. They'll puff up to stretch and tear the old skin, so that's normal. They'll be discolored as they're between old, dingy skin and the not yet fully exposed new skin. The hiding during the process is also normal since they know they're vulnerable all the while. (I don't think I'd want to do something like that out in the open either. ) They'll also be stiff before and during a shedding again, owing to the old, relatively dry skin being shed. The substrate caking onto the old skin is very likely depending upon what it is. That you can easily make a positive change of right away to help the little guy, so not a dire emergency as long as he hasn't ingested enough to impact his gut.
Seems like he's just had a particularly arduous shed this time. Maybe change their habitat to help them avoid the caking of substrate on old skin problem but otherwise he should be fine once he's done.
He actually looks quite good in your photos. Good color, robust stockiness, bright eyes. I'd say he's ok.

Also, they'll eat less prior to a shedding and they won't eat again until after they've been done for a little while, nothing to worry about there either. And always leave them alone to eat their skin, they need it.

Almost forgot, that "something pink" hanging out of his mouth is his tongue.