Cast a copy of Channel by paying {G}{G}.
Activate the ability granted by Channel by paying 1 life, adding {C}.
Repeat step 2 as desired.
Cast Comet Storm by paying {R}{R} and all remaining available mana, dealing a large amount of damage to a set number of targets.

Near-infinite damage

Yavimaya Bloomsage // Channel

Comet Storm

Activate Tree of Perdition by tapping it, swapping its toughness with an opponent's life total.
Cast Comet Storm by paying {3}{R}{R}, dealing 3 damage to the opponent.
Cast Hidetsugu's Second Rite by paying {3}{R}, dealing 10 damage to the opponent.
The opponent loses the game due to having zero life.

Combos with "Comet Storm"