Edit: To write a more meaningful message, there is a twitter thread full of Racoon-san Mansion-themed speedrunning jokes and I'm loving it even though I need to use twitter's translate function to read them.
I think most likely it's a giant otter given their tactics of sending one forward Rat survived, otter #1 goes out, gets stuck in the calendar room, #2 and #3 head back for more cloning when she doesn't return
That being said, it being the small otter messing with buttons also makes a lot of sense