Bomb

You magically create a mark on a creature that will cause them to explode. Choose a creature that you can see within range. That creature must succeed a Charisma saving throw or be cursed. On a failed save, roll 1d6 + 1. The curse on the creature expires after a number of turns equal to the number that you roll, with the duration decreasing at the start of each of the cursed creature's turns. You must concentrate for that duration, and the target erupts into flames when the curse ends, causing the following effect:

All creatures within 20 feet of the target must make a Dexterity saving throw, taking 2d10 fire damage per turn that the curse was active, or half as much damage on a successful save. The cursed creature automatically fails this saving throw. If your concentration is ended early- or if the target exits the range of this spell, the cursed target still explodes but all damage dealt is halved. If the curse is removed or you choose to dispel it, this spell ends with no explosion.