Chandras Einäscherer

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.