Constant and Automatic Abilities

Certain abilities shouldn't use any actions. Auras are a common constant ability, with frightful presence, the pachinyam swarm's dust cloud, and the bloodbrother's frigid cold as notable examples. An aura needs a range, and if it needs a DC, you'll usually set it to the moderate spell DC unless the aura is one of the creature's defining concepts. For example, the liberoba's ultrasonic pulse DC is significantly higher because the aura is such an iconic part of the creature and necessary for it to see enemies. Abilities the creature has no control over should be automatic. For example, the cybernetic zombie explodes when it dies. It has no option not to, so this wouldn't make sense as a reaction or free action. Conversely, the Ferocity ability is a reaction because it requires the creature to give itself a last push to stay at 1 HP.