Sozin's Comet in hand or in exile (was foretold on a previous turn).
Easy Prerequisites
You and an opponent each control a creature.
Notable Prerequisites
You control a creature that can attack this turn and that cannot be blocked or killed by an opponent.
Mana Needed
({4} magic symbol) ({R} magic symbol) ({R} magic symbol) ({R} magic symbol) at most available.
Steps
Cast
The Last Agni Kai by paying ({1} magic symbol) ({R} magic symbol) .
Cast
Sozin's Comet either from your hand by paying ({3} magic symbol) ({R} magic symbol) ({R} magic symbol) or from exile for its foretell cost by paying ({2} magic symbol) ({R} magic symbol) .
Declare a creature as an attacker, triggering its firebending ability, adding ({R} magic symbol) ({R} magic symbol) ({R} magic symbol) ({R} magic symbol) ({R} magic symbol) .
Move to your postcombat main phase. You will not lose the mana due to
The Last Agni Kai.
Activate
Aggravated Assault by paying ({3} magic symbol) ({R} magic symbol) ({R} magic symbol) , causing you to untap all creatures you control and to get an additional combat and main phase after this one.
Repeat from step 3.
Notes
You can attack with multiple creatures to get infinite red mana. Depending on the boardstate, you can use the same creature to fight in step 1 and to attack with. You may also net red mana that can then reduce the overall cost and help pay for