Chandra Ablaze

You cast red instant cards and red sorcery cards from your graveyard as part of the resolution of Chandra Ablaze's third ability. You don't choose which ones to cast until you're actually doing so as the ability resolves. You cast only the ones you want to, and you may cast them in any order. Timing restrictions based on the card's type (if it's a sorcery) are ignored. Other restrictions are not (such as "Cast [this card] only during combat"). Each card you cast this way is put on the stack, then the ability finishes resolving. Those spells will then resolve as normal, one at a time, in the opposite order that they were put on the stack. They'll go back to the graveyard as they resolve.

If you activate Chandra Ablaze's first ability, you don't discard a card until the ability resolves. You may activate the ability even if your hand is empty. You choose a target as you activate the ability even if you have no red cards in hand at that time.

If you cast a card "without paying its mana cost," you can't pay any alternative costs. You can pay additional costs, such as kicker costs.