Necromantic Physiology

Your unusual physiology has developed in a way that makes it difficult for parasites and other infestations to prey upon you. You gain a +2 circumstance bonus to saving throws against diseases. If you roll a success on a saving throw against a disease, you get a critical success instead. If you have a different ability that would improve the save in this way (such as the fighter class feature), if you roll a critical failure on the save you get a failure instead.