Entity: Sewer Rat

Source Player Core 2 pg. 29 ^1.1

You come from a long line of ratfolk with a community based in the sewers beneath a large settlement. You are immune to the disease putrid plague. You gain a +1 circumstance bonus to saving throws against diseases and poisons. If you roll a success on a saving throw against a disease or poison, you get a critical success instead. If you have a different ability that would improve the save in this way (such as the battle hardened fighter class feature), if you roll a critical failure on the save you get a failure instead.