From the official release post - "Burn Eternal, Spirit Fire Brand" :
"He calls to them. He calls for strength and power absolute. He reaches out to the spirits. They reach back. Burn. They fuel his fury. Burn. They sharpen his rage. Burn. He submits to the fire. Burn. He submits to flame. Burn. The spirits demand sacrifice. Burn. Burn the world.
Summon Spirit Fire Brand, now available in the League store for 975 RP until October 26 23:59 PDT(1350 RP after that).