Boomer Zombie

Undead Fortitude. If damage reduces the zombie to 0 hit points, it must make a Constitution saving throw with a DC of 5 + the damage taken, unless the damage is radiant or from a critical hit. On a success, the zombie drops to 1 hit point instead.

Pus Sacs. If a Boomer takes piercing damage one of its pus sacks burst and creatures within 5 ft take 1d4 poison damage. if the piercing damage is critical then the boomer uses the attack Explosion. a pus sack also bursts if slashing damage done to it is critical.

Slam. Melee Weapon Attack: +3 to hit, reach 5 ft., one target. Hit: 4 (1d6 + 1) bludgeoning damage. 

Explosion. If the Boomer is in melee range with an enemy it will explode as an action, killing itself in the process, and every creature in a 10 ft. radius must make a DC 13 Dex saving throw or take 15 (3d6 + 3) Poison Damage + 7 (1d8 + 2) Force Damage on a failed save and half as much on a successful save. One a failed save each target must make a DC 13 Con saving throw. On a failure it is poisoned for the next 3 rounds. At the end of a creature's turn it can reroll the saving throw and the poison ends earlier on a success In addition the poison contains pheromones that attract other Zombies. If a target is hit by the poison, every zombie in a 80 ft radius focuses the targets for the next 5 round. The zombies automatically know the location of the targets. The Boomer also explodes if it dies. The poison has no effect on other undead creatures.