The material below is Open Game Content from a 3PP Source
Self-Destruct (Su): An eidolon can explode, killing itself, and it automatically explodes when other creatures kill it. Select acid, cold, electricity, or fire. When the eidolon explodes, it deals 1d6 points of damage of the selected type per HD it possesses in a 20-foot radius. Those caught in the explosion can attempt a Reflex saving throw (DC 10 + one-half the eidolon’s HD + the eidolon’s Constitution modifier) for half damage.