Unholy Heat
Instant
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.
"The devils use fire. Why shouldn't we?"
Kari Christensen
Rulings
The 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.
(wotc • 2021-06-18)
Unholy 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.
(wotc • 2021-06-18)
Related Cards
Printings
Rulings
The 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.
(wotc • 2021-06-18)
Unholy 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.
(wotc • 2021-06-18)