inside no. 9 S05E01 spoiler, ,mystery mascot poll thing
Just so I don't leave you hanging:
There is no canonical answer. The characters in the episode explicitly disclaim that it's an otter, supposedly because of the ears, but there's no indication whether they're right. FWIW, I'd guessed otter, too. I was just curious what everybody else thought. 'cause yeah, damned if that's not an otter. :)