Walking Bomb

You touch an object or creature, making a melee spell attack against the target. On a hit, you transmute the air surrounding them into a tiny bubble of pure oxygen inside the target. When the spell ends, the bubble ignites, creating a small explosion and dealing 1d8 fire damage.

The spell's damage increses by 1d8 when you reach 5th level (2d8), 11th level (3d8), and 17th level (4d8)