Amanuensis wrote:
How is radiation different from mutant?
I think the mutant template gets most of the way there, but a mutant isn't inherently radioactive.
One easy route: steal abilities from irradiated dead. Strip off the monster stats and undead traits, scale its abilities to the creature's base CR, and give it STR/CHA mods to make it a quick and dirty +2/+3 CR template.
That said, standard radioactivity itself is a pretty powerful poison that deals a minimum of 1 Con drain. A radioactive aura could also do it (and make detect radioactivity pretty useful). Since it sounds like the creature would give off a more passive form of radioactivity, the aura could instead deal only the secondary radiation damage (Strength damage instead of Con drain), especially at low levels, without needing to water down the poison save DC. A similar option would be to give it irradiate as a spell-like ability.
If radioactivity is common where the creature would be encountered and the PCs are prepared for it—say the PCs are wearing protective gear while encountering radioactive creatures—there are other neat spaces you could play with, like radioactivity effects acting as positive energy for the creature, powerful ambient radioactivity granting temporary hp or combat bonuses despite the ability-score damage, or poison- and radioactivity-curing effects dealing damage or negative conditions.
I'd also expect them to glow, or at least have the ability to emanate non-magical light at will.
