Mire Fiend

Amphibious. The mire fiend can breathe air and water.

Demonic Resilience. The mire fiend is resistant to cold, fire, and lightning damage. In addition, it is immune to poison damage and to the poisoned condition.

Magic Resistance. The mire fiend has advantage on saves against spells and other magical effects.

Pack Tactics. The mire fiend has advantage on attack rolls against a creature if at least one of the mire fiend's allies is within 5 feet of the creature and the ally isn't incapacitated.

Swamp Camouflage. The mire fiend's Stealth is 21 while in swampy terrain.

Multiattack. The mire fiend makes one Mandibles attack, one Spear attack, and one Stinger attack.

Mandibles. _Melee Weapon Attack:_ +6 to hit, reach 5 ft., one creature. _Hit:_ 12 (2d8+3) slashing damage.

Spear. Melee Weapon or Ranged Attack: +5 to hit, reach 5 ft. or range 20/60 ft., one target. _Hit:_ 5 (1d6+2) piercing damage, or 6 (1d8+2) piercing damage if used with two hands to make a melee attack.

Stinger. _Melee Weapon Attack:_ +6 to hit, reach 10 ft., one creature. _Hit:_ 5 (1d4+3) piercing damage plus 10 (3d6) poison damage, and the target must succeed on a DC 14 CON save or be poisoned.

Stunning Snap (Recharge 5-6). If the mire fiend has no creature grappled, it snaps its mandibles together with great force, creating a miniature sonic boom in a 30-foot cone.<br>Each creature in that area must make a DC 14 CON save. On a failure, a creature takes 21 (6d6) thunder damage and is stunned until the end of its next turn. On a success, a creature takes half the damage and isn't stunned.

Acidic Retribution. When the mire fiend takes damage, including any damage that reduces it to 0 HP, it can expel acid from its stinger in a 15-foot line that is 5 feet wide. Each creature in that line must make a DC 14 DEX save, taking 10 (3d6) acid damage on a failed save, or half as much damage on a successful one.