User blog comment:BunsenH/Monsters: boy or girl? Male or female?/@comment-27661991-20170715185644

I think there may be at least one exception; Shugabush. In Kristian Bush's post announcing the Shugabush as part of a collab, Kristian consistently calls the then-new character "him" and refers to Shugabush as, effectively, being "me";

"Soon, the team at Big Blue Bubble (the game developers) had imagined all sorts of stuff: the monster's name, what he likes, how to breed him (hint: Bowgart + Clamble), what to feed him, amazing details"

Source: Monster Monday: Kristian collaborates with My Singing Monsters to create the Shugabush!