The lightning skitters over the Slaad's resistant hide, but in the brief heartbeat between the stroke and the sound, Ttharg, you feel a thrum from the vial of holy water; and then the loudest sound any of you have ever heard rips across the swamp and devastates the Slaad.
Spoiler: OOCBahamut transmutes the lightning to thunder damage. Everyone is deafened for 1d4 (4) rounds.