Microlite20

To create new monsters, assign Hit Dice (d8 for most things, d12 for Dragons and Undead). Attack bonus and skill level = number of Hit Dice. If it’s an intelligent critter, +3 bonus to one skill. Assign stats to suit. Equip and add abilities as required.

Critters is a random monster generator for Microlite20 which generates a random name and set of stats. What the creature looks like, what it's weapon or natural attacks are and how it behaves is entirely up to you - consider it an inspiration tool for those times when you want something not in any Monster Manual or the SRD.