Bloatbomb

You take 1 action to begin casting Bloatbomb on a target you can see, you must maintain concentration until your next turn, where you take 1 action to detonate the corpse.

You cause the corpse of a freshly killed corporeal creature, (killed within the previous hour),  to immediately begin to internally rot.  This causes the body to bloat and expand until it explodes in a gory shower of viscera causing 2d8 necrotic damage to all creatures within a 10 foot radius, and 1d8 necrotic to those in the 10 to 15 foot radius.  A successful CON saving throw will reduce the damage by half (rounding down).

For each spell slot used higher than 2, add 1d8 to the damage rolled.