Venomous Retribution. When a melee attack strikes the Abathmaab the attacker must make a DEX save DC 13.  On a failed save they take d4 Acid & d4 poison damage.  On a successful save they take half this damage.  

Spellcasting. The Abathmaab is a 3rd level spellcaster. Its spellcasting ability is Intelligence (spell save DC 13, +4 to hit with spell attacks). The Abathmaab has following Wizard spells prepared:
Cantrips (at will): Poison Spray, Acid Splash
1st level (3): Grease, Ray of Sickness 

2nd level (2): Web, Hold Person

Needle Burst.  Recharges on 6. The Abathmaab expands its many venom sacks & expels a burst of envenomed quills.  Creatures within 15' must make a Dexterity save DC 13 or take 2d6 piercing damage & become Poisoned.  Characters who pass the save take half the damage and are not poisoned.  

Action Melee Attack. Envenomed Quill: +4 to hit, reach 10 ft., 1 target. Hit: 4 (1d6 + 1) Piercing damage + 8 (2d6+2) Poison damage. 

Action Ranged Attack. Thrown Quill: +4 to hit, range 30 feet, 1 target. Hit: 4 (1d6 + 1) Piercing damage + 8 (2d6+2) Poison damage. 

Bilious Spray. If an attack brings the Abathmaab to 5 HP or fewer it sprays the contents of its many bladders in a terrific gust which strikes all creatures within 5 feet of it.  Creatures must make a Constitution save DC 13 or become Poisoned.