Alchemist's fire (COS)

This sticky, adhesive fluid ignites when exposed to air. As an action, you can throw this flask up to 20 feet, shattering it on impact. Make a ranged attack against a creature or object, treating the alchemist's fire as an improvised weapon. On a hit, the target takes 2d4 fire damage at the start of each of its turns. A creature can end this damage by using its action to make a DC 10 Dexterity check to extinguish the flames.
Alchemists' fire will burn any flammable items that aren't being carried it touches, and if it lands on an object or space it remains there for 1 minute, any creature that passes through its space must make a DC10 Dexterity saving throw or take (1d6) fire damage, a creature can take this damage once per round from each vial.