Fungus is a character that appeared in the Riders of Berk series.

He's a sheep and Mildew's pet. Fungus is probably not only a pet to Mildew as the old viking speaks to this sheep more than to someone else and it is clear that Mildew cares for Fungus, probably the living one the vikings cares most about, also having one of his pictures o his wall besides the ones of his deceased wives. Fungus, of course, lives with Mildew in a small house on the outskirts of Berk.