Acid Burn. If a creature wearing metal armor or holding a metal weapon is dealt acid damage from one of the glavenus's attacks, that creature must succeed on a DC 21 Dexterity saving throw. On a failed save, one of the following effects happen:

• Armor. The armor takes a cumulative -1 penalty to the AC. Nonmagical armor reduced to an AC of 10 is destroyed. Magical armor reduced to an AC of 10 no longer gains the benefits of any of its properties for one week, but its AC returns to normal after a long rest.
• Weapon. The weapon takes cumulative -1 penalty to its attack and damage rolls. A nonmagical weapon reduced to -5 to its attack or damage is destroyed. A magical weapon reduced to -5 no longer gains the benefits of any of its properties for one week, but it becomes a +0 weapon after a long rest.

Glavenus Tail. The glavenus can use its bonus action to sharpen its tail, removing the acidic crystals that cover it; or it can use the bonus action to regrow them.

Legendary Resistance (3/Day). If the glavenus fails a saving throw, it can choose to succeed instead.

Multiattack. The glavenus makes two Tail attacks. If both attacks hit the same target, the target also takes 14 (4d6) slashing damage and must succeed on a DC 21 Strength or Dexterity saving throw (target's choice) or be knocked prone.

Bite. Melee Weapon Attack: d20+13 to hit, reach 5 ft., one target. Hit: 26 (3d12 + 7) piercing damage + 7 (2d6) acid damage.

Tail (Acid Crystals Only). Melee Weapon Attack: d20+13 to hit, reach 15 ft., one target. Hit: 23 (3d10 + 7) slashing damage plus 7 (2d6) acid damage.

Tail (Sharpened Only). Melee Weapon Attack: d20+13 to hit, reach 15 ft., one target. Hit: 40 (6d10 + 7) slashing damage.

Tail Spin (Recharge 5-6) The glavenus uses one of the following tail spin attacks depending on which form its tail is in:

• Acid Tail Spin. The glavenus moves up to 50 feet in a straight line while spinning, without provoking opportunity attacks, while striking each creature in a 15-foot radius of its path with its tail. Each creature in that area must make a DC 21 Dexterity saving throw, taking 24 (7d6) slashing and 24 (7d6) acid damage on a failed save, or half as much damage on a successful one.
• Sharpened Tail Spin. The glavenus moves up to 50 feet in a straight line while spinning, without provoking opportunity attacks, while striking each creature in a 15-foot radius of its path with its tail. Each creature in that area must then make a DC 21 Dexterity saving throw, taking 63 (18d6) slashing damage on a failed save, and half as much damage on a successful one.