Chandra's Incinerator
Creature — Elemental
This spell costs 
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, this creature deals that much damage to target creature or planeswalker that player controls.
Craig J Spearing
Core Set 2021 (M21)
• #136Rulings
In a multiplayer game, Chandra's Incinerator counts damage dealt to opponents who have lost the game.
(wotc • 2020-06-23)
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.
(wotc • 2020-06-23)
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}.
(wotc • 2020-06-23)
The cost reduction applies only to generic mana in the cost of Chandra's Incinerator. It can't reduce the {R} requirement.
(wotc • 2020-06-23)
Rulings
In a multiplayer game, Chandra's Incinerator counts damage dealt to opponents who have lost the game.
(wotc • 2020-06-23)
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.
(wotc • 2020-06-23)
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}.
(wotc • 2020-06-23)
The cost reduction applies only to generic mana in the cost of Chandra's Incinerator. It can't reduce the {R} requirement.
(wotc • 2020-06-23)