Isabelle
Isabelle may look like a little snufflybean and may seem like she is 100% innocent and a good person, but we all know that is not the case. In her spare time, she likes to brutally murder other people in Smash and kill the planet with her car exhausts in Mario Kart. We all know it. We're not fools. We see her menacingly lurking in that corner with her fishing rod, waiting to stike. We see her aggressively t-posing on innocent civilians.
Honestly though, Isabelle is a pretty cool character. She works as your assistant in most of the games and doesn't even expect any pay for her work. She's meant to be a Shih Tzu in the game and her name comes from the currency in the series, bells.
She provides very helpful services in the morning announcements in New Horizons, including informing us about her TV habits and when she finds missing socks. I wonder if she watches MagLevs in Love? I've heard MagLev Mike took his relationship off the rails.