I see lots of magical items, now for some low-magic tiny animals...
Metal worm – eats through small amounts of metal such as a within a keyhole or the clasp of a chain once per day before becoming full, prefers it rusty. Can be taught to eat through other substances as trained.
Honeyed bee – a bee both larger than normal and more intelligent than normal, when surrounded by wildflowers will return and make honey for the owner it is devoted to. Can be selectively trained to collect certain wildflowers each level, with the resultant honey beneficial for being a salve to wounds, detecting poisons, or flavouring drinks, etc.
Listening spider – spins a small amount of web once per day that transmits the smallest vibrations and allows you to determine basic speech or sounds detected at the other end of the web. Generates increasingly more complex structures with it’s web as it is trained.
Shifting newt – raised amongst Moon Ruins the newt momentarily disappears then reappears nearby when touched. Can be taught to disappear and reappear with increasingly complex instructions as trained.
Singing cricket – can be taught a single word or short tune it then repeatedly produces on command. Number of words and tunes increases with training.
Pinecone
firefly – has a small spark capable of igniting flammable materials on contact.
Needs to be kept in a jar without training, but training improves the command
and range it can fly.