Colesons Infectious Flame

You produce a lively bead of flame which attempts to seek out living creatures, and send the bead of flame towards a creature within range which attempts to latch on to and burn that creature. The target must make a dexterity saving throw or be engulfed in flame. While engulfed in flame, at target gives off 10 feet of bright light and 10 feet of dim light, and takes 2d8 fire damage at the start of each of its turns. On a successful saving throw, the target does not become engulfed. A creature which moves within 5 feet on a engulfed creature on its turn or end it's turn within 5 feet of an engulfed creature must make a dexterity saving throw or also become engulfed. A creature can use an action to attempt to make a dexterity saving throw to end the effect on themselves or a creature within five feet of them, ending the effect on a success.

Casting with higher-level spell slots: When cast witha spell slot of 4th level or higher, increase the damage of the spell by 1d8 for each spell level above 3rd