Source: Familiar Folio, pg(s). 29
Caypups resemble rust-red mastiff puppies with piercing blue eyes. They measure four feet long, weigh 75 pounds, and never mature past adolescence.
Caypups can be found in both Elysium and the Material Plane, and are driven to do good and fight evil wherever they go. They sometimes join adventurers or become familiars in the hope of emulating their ancestor Thunder and his master Cayden Cailean.