Only occasionally, in a small region known as Darkroot Garden. They're not much of a threat if you steer clear of them and their...children, I suppose. There are little ones that aren't nearly as dangerous, at any rate.

[He wasn't entirely sure how mushroom people reproduced, and was happy to stay ignorant on that fact.]

The real threats were the stone guardians and the ents. Giant white and red mushroom people are easy to pick out from afar in the middle of a forest. Moss-covered stone giants and plant people, not quite as much.