According to Wild insider Mike Russo, Fleury described the creature as a "wild beast with his mouth open" and said the design was inspired by former NHL goaltender Andy Moog, who famously played for the Edmonton Oilers, Boston Bruins, Dallas Stars, and Montreal Canadiens during a 713-game NHL career.
If you've never seen Moog's mask, which he wore while playing for the Boston Bruins as a goalkeeper, here's a terrific photo of it: