When reading a monster stat-block I noticed some spell-like abilities list a percent after the description. Does this mean that only X% of these monsters have this ability? If not, can you please tell me what it means?
For example, the Mephits' stat-block has this:
Spell-Like Abilities (CL 6th) 1/day—summon (level 2, 1 mephit of the same type 25%)