Looking back through 'em, we have several precedents that might fit...
Sparks (Ex): A will-o’-deep attacks wlth a series of small, white-hot sparks. It may unleash up to four sparks as a full attack action. These sparks are ranged touch attacks with no range increments and a maximum range of 10 feet.
Lethal Shock (Su): Every 1d4 rounds, a will-o'-mist can release a lethal shock. This effect has a radius of 30 feet, centered on the will-o'-mist. The shock deals 2d8 points of electricity damage. A DC 15 Reflex save reduces the damage by half. The save DC is Constitution-based.
Lightning Bolt (Su): Once every 1d3 rounds, a will-o'-sea can unleash a 120-foot-long line of lightning that deals 10d6 points of electricity damage (Reflex DC 22 halves this damage). The lightning bolt sets fire to combustibles and damages objects in its path. It can melt metals with a low melting point, such as lead, gold, copper, silver, or bronze. If the damage caused to an interposing barrier shatters or breaks through it, the bolt may continue beyond the barrier if the range permits; otherwise, it stops at the barrier just as a spell effect does. The save DC is Constitution-based.