Blister Beetle

Blistering Aura. At the start of each of the blister beetle's turns, each creature within 5 feet of it takes 21 (6d6) acid damage. Nonmagical armor and weapons in the aura are partially dissolved, taking a permanent and cumulative -1 penalty to the AC they provide or to their damage rolls, respectively. Nonmagical armor is destroyed if the penalty reduces its AC to 10. A nonmagical weapon is destroyed if its penalty drops to -5. A creature that touches the blister beetle or hits it with a melee attack while within 5 feet of her takes 10 (3d6) acid damage.

Spider Climb. The blister beetle can climb difficult surfaces, including upside down on ceilings, without needing to make an ability check.

Multiattack. The blister beetle can make three ranged or four melee attacks, but can use its bite only once.

Bite. Melee Weapon Attack: +11 to hit, reach 5 ft., one target. Hit:  24 (3d12 + 5) piercing damage plus 28 (8d6) acid damage.

Claw. Melee Weapon Attack: +11 to hit, reach 10 ft., one target. Hit: 19 (3d10 + 5) slashing damage.

Acid Spit. Ranged Weapon Attack: +8 to hit, range 80 ft./120 ft, one target. Hit: 28 (8d6) acid damage. In addition, nonmagical armor worn by the target is partly dissolved and takes a permanent and cumulative -1 penalty to the AC it offers. The armor is destroyed if the penalty reduces its AC to 10.