Unholy Heat is a rare Instant card from Secret Lair Promo (SLP), collector number 4. Current market price: $1.24 (foil $7.62), TCGplayer market prices via Scryfall.
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.