Cheapest priced copy (Mystery Booster 2): $0.35 at Card Kingdom, near mint, their price list as of .
Unholy Heat 
Instant · Rare · Secret Lair Countdown · #70
Unholy Heat deals 2 damage to target creature or planeswalker.
Delirium — Unholy Heat deals 6 damage instead if there are four or more card types among cards in your graveyard.
Legal inCommanderModernLegacyVintagePauper
Not legal inBrawlStandardPioneer
7 printings · $0.35 to $11.99 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Modern Horizons 2 Timeshifts | 13 | Common | $1.79 | $0.99 |
| Mystery Booster 2 | 63 | Common | $0.35 | — |
| Modern Horizons 2 | 145 | Common | $0.35 | $0.49 |
| Outlaws of Thunder Junction Commander | 182 | Common | $0.35 | — |
| Secret Lair Countdown | 70 | Rare | — | — |
| Secret Lair Promo | 4 | Rare | $2.29 | $5.99Out of stock |
| Special Guests | 71 | Mythic | $2.99 | $11.99 |
2 rulings from Wizards of the Coast
- 18 June 2021The card types that can appear in a graveyard are artifact, battle, creature, enchantment, instant, kindred, land, planeswalker, and sorcery. Legendary, basic, and snow are supertypes, not card types; Kavu and Equipment are subtypes, not card types.
- 18 June 2021Unholy Heat checks your graveyard as it resolves to determine if it deals 2 or 6 damage. At that time, Unholy Heat isn't in the graveyard yet.