MUTATIONS
While a mutation can assume many forms, it typically signifies an abnormal trait or ability not common to the species. Mutations can be pronounced or unnoticeable. They may grant extraordinary abilities or effect subtle to grotesque changes in a creature’s physiology.
Mutations may appear only at birth or manifest as consequences of radiation exposure or some horrible physical trauma.
Whenever a creature or NPC gains a mutation, the GM may roll percentile dice and consult Table: Mutations below, then select an appropriate number of drawbacks with a total MP value equal to or greater than the MP cost of the randomly determined mutation.
All special qualities granted by mutations are considered extraordinary abilities. Using an extraordinary ability is a free action unless noted otherwise.
MUTATION POINTS
Mutation Points (MP) provide a simple method of selecting mutations while preserving game balance. All creatures (including player characters) begin to play with 0 MP. A creature gains MP by selecting one or more drawbacks—physical deformities and disabilities that make the creature less effective in play. A creature can then “spend” the MP on one or more beneficial mutations. The total MP spent on beneficial mutations cannot exceed the total MP the creature gains from drawbacks. A creature may still have unspent MP after choosing beneficial mutations, however. These unspent MP can be spent on new mutations at a later time.
Saves
So depending on the strength of the effect that is mutating you the saves are as followed:
DC 5 Weak, Pure Strain immune
DC 10 Moderate Pure Strain +5 to save
DC 15 Strong
DC ** Automatic Failure. Pure Strain save with DC 25
A single source can only affect one subject once every 12 hours period. You get +1 vs other sources for the next 12 hours. You can stack the bonus up to your Con bonus against the different sources over the same 12-hour time.
To roll for the mutation please use this website, he has already a nice page setup for these so just go there and use ONLY that page, nothing else on that page is being used unless a link is posted here.
mutations-article
