Cheapest priced copy (Hour of Devastation): $0.49 at Card Kingdom, near mint, their price list as of .
Wildfire Eternal 
Creature — Zombie Jackal Cleric · 1/4 · Rare · Hour of Devastation · #109
Afflict 4 (Whenever this creature becomes blocked, defending player loses 4 life.)
Whenever this creature attacks and isn't blocked, you may cast an instant or sorcery spell from your hand without paying its mana cost.
Legal inCommanderPioneerModernLegacyVintage
Not legal inBrawlStandardPauper
3 printings · $0.49 to $1.79 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Hour of Devastation | 109 | Rare | $0.49 | $0.49 |
| Hour of Devastation Promos | 109 | Rare | — | $0.49 |
| Hour of Devastation Promos | 109s | Rare | — | $1.79 |
8 rulings from Wizards of the Coast
- 14 July 2017Wildfire Eternal's second ability resolves before combat damage is dealt, and you must cast a spell at that time if you wish to cast one without paying its mana cost. You can cast a sorcery during the declare blockers step this way.
- 14 July 2017If multiple creatures block a creature with afflict, afflict triggers only once.
- 14 July 2017If the card has {X} in its mana cost, you must choose 0 as the value of X when casting it without paying its mana cost.
- 14 July 2017Afflict resolves before combat damage is dealt. If this loss of life brings a player to 0 life or less, that player loses the game immediately. A blocking creature with lifelink won't deal combat damage in time to save that player.
- 14 July 2017An ability that triggers when something "attacks and isn't blocked" triggers in the declare blockers step after blockers are declared if (1) that creature is attacking and (2) no creatures are declared to block it. It will trigger even if that creature was put onto the battlefield attacking rather than having been declared as an attacker in the declare attackers step.
- 14 July 2017Afflict causes the defending player to lose life; it's not damage or combat damage.
- 14 July 2017If you cast a card "without paying its mana cost," you can't pay any alternative costs. You can, however, pay additional costs. If the card has any mandatory additional costs, such as that of Tormenting Voice, those must be paid to cast the card.
- 28 July 2023If a creature is attacking a planeswalker, that planeswalker's controller is the defending player. If a creature is attacking a battle, that battle's protector is the defending player.