Green-Flame Blade

You brandish the weapon used in the spell's casting and
make a melee spell attack with it. On hit, the target suffers the weapon attack's normal effects and you can cause green fire to leap from the target to a different creature of your choice that you can see within 5 feet of it. The second creature takes fire damage equal to your spellcasting ability modifier.

Both damage rolls increase by 1D8 fire damage at 5th, 11th and 17th level.