Chandra's Incinerator

This spell costs {X} less to cast, where X is the total amount of noncombat damage dealt to your opponents this turn.
Trample
Whenever a source you control deals noncombat damage to an opponent, Chandra's Incinerator deals that much damage to target creature or planeswalker that player controls.

Core Set 2021

Core Set 2021 Promos

Chandra's Incinerator counts all noncombat damage dealt to your opponents, not the difference in their life totals since the turn began. For example, if an opponent was dealt 5 noncombat damage but gained 3 life, Chandra's Incinerator still costs just {R}.

Combat damage is the damage that's dealt automatically by attacking and blocking creatures. Any other damage is noncombat damage, even if it's dealt during a combat phase by an attacking or blocking creature.

In a multiplayer game, Chandra's Incinerator counts damage dealt to opponents who have lost the game.

The cost reduction applies only to generic mana in the cost of Chandra's Incinerator. It can't reduce the {R} requirement.