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.
The Omen Star: In the West, in what appears to be an eccentric orbit, appears the Omen Star. The appearance of the Omen Star in the first house of the sky bodes "great things" for good or ill are about to happen. It is the rest of the stars that determine if it is for good and ill. Thus people are always looking for things to happen during the time of the Omen Star.