For Chandra Acolyte of Flame's -2 ability, you can cast an instant or sorcery card with mana cost 3 or less from your graveyard. Do you have to pay that card's mana cost?
In general, if you cast a card due to Chandra's last ability, you still must pay its mana cost and any other costs required (C.R. 601.2f, 601.2h). (The ability doesn't say, for example, "...without paying its mana cost" — compare the second ability of Chandra, Pyromaster with her third ability.)
Does Chandra Acolyte of Flame's -2 cost mana?