What if some crazy wizard created an artifact that empowered rodents that touched it with one random supernatural power? Preferly right out of the pages of your favorite four-color. (But only one power!) This item does not convey any sort of intelligence boost.
Somewhere along the line, someone very powerful lost their marbles. Literally. Possessing a marble allows incredible clarity of thought about a particular related subject.
Dwarven Mountain Pony - a small, and hardy animal well suited to living in the mountains and highlands. Able to subsist on grass and brush, with hard hooves, and nimble feet. The dwarves use them as pack animals, and to pull ore carts, and to drive bellows for their furnaces. Never ridden as dwarves like to keep both feet firmly on the ground. As stubborn and tough as the dwarves themselves. Also only about 12 hands tall (1 hand=4 inches)