Fire Serpent (5e Creature)
From D&D Wiki
Large elemental, unaligned
Bite. Melee Weapon Attack: +5 to hit, reach 5 ft., one target. Hit: 10 (2d6 + 3) fire damage.
A fire serpent is an elemental being of fire and lava given a physical shape through magic like the moat of lava spell. They are incredibly aggressive, attacking anything that draws too close.