The Royal Capacitor is an unlockable Equipment in Risk of Rain 2.
Completing the Ascendant Challenge unlocks this item.
Activating the Capacitor calls down a bolt of lightning on a targeted enemy. It can't be activated if an enemy is not being targeted, and the blue "Q" reticule must appear on the target. It deals 3000% damage to that enemy, with the possibility of a critical strike. It is a powerful weapon because the cooldown is a relatively short 20 seconds, and it cannot miss.