Mousefolk derive from ill-advised tampering with the genome of home sapiens by the Visitors, hundreds of thousands of years ago. Mousefolk mature from birth to adulthood in about five years. Although about halfling height, they nevertheless have a movement rate of 30' when unencumbered. Generally weighing 50 to 60 pounds, they tend to be lithe.

The lifespan of a Mousefolk is 100 to 130 years. Mousefolk are immune to fear effects, even supernatural ones such as a dragon's fear aura. Mousefolk, given adequate time, can chew through anything if its hardness is less than that of their teeth.

Mousefolk begin play with with traits Excellent Hearing +1 and with All Mouse, No Rodent +1. A player may opt to have her 1st level Mousefolk character raise this to either +2 or +3.

Most classed Mousefolk are Rangers or Paladins, as they tend toward a nobleness of spirit.

If using Moldvay saving throws, Mousefolk have the same saves as Halfings.