Cavalier of Flame is a mythic Creature — Elemental Knight card from The List (PLST), collector number M20-125. Current market price: $1.17, TCGplayer market prices via Scryfall.
{1}{R}: Creatures you control get +1/+0 and gain haste until end of turn. When this creature enters, discard any number of cards, then draw that many cards. When this creature dies, it deals X damage to each opponent and each planeswalker they control, where X is the number of land cards in your graveyard.