Death Burst

The creature explodes when it drops to 0 hit points. Each creature within 20 feet of it must succeed on a DC 15 Constitution saving throw or take X poison damage and become infected with a disease on a failed save. Target’s immune to the poisoned condition are immune to this disease. Spores invade an infected target’s system, killing the target in a number of hours equal to 1d12 + the creature’s Constitution score, unless the disease is removed. In half that time, the creature becomes poisoned for the rest of the duration. After the target dies, it sprouts 2d4 Tiny gas spores that grow to full size in 7 days. (Gas Spore, pp. 138, MM)