Azula, Cunning Usurper

You pay the costs for an exiled card if you cast it. You may pay any alternative costs the card has rather than the card's mana cost.

Firebending abilities aren't mana abilities. They use the stack and can be responded to.

Any other mana you add during combat will still be lost as normal when moving between steps of combat.

Mana from firebending abilities isn't lost until you leave combat and go to your second main phase. It can be used at any time during combat, even after combat damage has been dealt.

Casting an exiled card causes it to leave exile. You can't cast it multiple times.

The six types of mana are white, blue, black, red, green, and colorless.

Multiple instances of firebending on the same creature trigger separately, each granting you the appropriate amount of mana.

"Firebending N" is a keyword that represents the ability "Whenever this creature attacks, add N {R}. Until end of combat, you don't lose this mana as steps end."