Combustion (5e Spell)
From D&D Wiki
This spell triggers on a reaction taken against a creature within 5ft that made a melee attack against you. Make a melee spell attack against the creature. On a hit, the target takes 2d6 fire damage.
At higher levels. This spell's damage increases by 1d6 when you reach 5th level (3d6), 11th level (4d6), and 17th level (5d6).