crafts, and knitting sometimes
Maffi is a SNES mouse! She has a SNES controller cable for a tail, and she can plug it into computers in order to interface with them. This mostly amounts to moving the mouse cursor around exactly how she wants it, just as easy as if it were a body part. Having perfect mouse cursor precision means she's very well-equipped to do digital art, and she does it as her "job" and hobby.
Another thing Maffi's tail can do is allow her to enter computers, and anyone holding onto her can come with her! If it's connected to the Internet she can traverse the network and cyberspace.
Aside from her tail, she has the ability to apply "affine transformations" to things - that is, she can apply geometric transformations like scaling, translation, rotation, flipping, etc. to objects or sometimes people, with limitations. When she applies an affine transformation to something, a transformation matrix appears in the air that she can manipulate with her fingers. She mostly just uses this to scale herself down when she wants to be a tiny mouse.
Maffi is a cute, shy nerd who's still very open to making friends and getting to know people, and she loves learning for the sake of learning, and often this helps her out because little bits of information she remembers reading can come in handy. She loves creating things, and in addition to art she likes to do crafts, and she can program and write Verilog too (which comes in handy when making things to use with her tail). She teams up with Nova to make video games about their past adventures.
Maffi has an inventory, which she can store files and items inside. It's structured like a computer filesystem, with a tree of folders. It has a search feature.
Some extended character information (tail info and stuff?) on my site!