He has 2 masks. First one pays homage to St. Louis and past goalies. The 2nd one is more "fun" with cartoon characters. Lucky Luc is his favorite.
According to The Goalie Guild: David Arrigo was the artist of both Halak masks. "The home mask has a classic rendition of the famous Gateway Arch and St. Louis skyline on the right side. Former Blues netminders Jaques Plante, Mike Liut and Grant Fuhr are on the left side. The top of the mask has the Bauer mark sprayed in a light blue, then “St. Louis Blues” written in script and goldleaf above it, then finally a small primary Blues logo just above that. The chin drop has the number 41 encased in a circle with two reversed bluenotes inlaid with more goldleaf."