Azilzena, the Burrower, Protectora

Tunneler. Azilzena can burrow through solid rock at half its burrow speed and leaves a 10-foot-diameter tunnel in its wake.

Natural Antidote. Azilzena is normally resistant to poison damage and immune to the poisoned condition. Their venom glands can also produce an extremely potent antidote that can grant this effect if ingested. However, if they take more than 20 poison damage (after resistance) from a single attack, this resistance ceases to function until the beginning of their next turn, and they are no longer immune to the poisoned condition, though they still make saves against effects that would cause that condition with advantage. If this happens three times, they lose poison resistance and poisoned immunity for 24 hours.

Blindsenser. Azilzena has incredibly adept hearing and can detect and pinpoint vibrations with great accuracy. However, this makes them vulnerable to loud noises. They make saves against spells or effects that deal thunder damage with disadvantage, and if a single attack or effect deals them more than 40 thunder damage (after vulnerability), they become stunned until the beginning of their next turn.

Slow Starter. In the first round of combat, Azilzena can only take the Dash action and must use it to increase their burrowing speed. They take no legendary actions during this round. However, during the second round of combat, if they use Emerge, they can immediately also use Sandblast.

Multiattack. Azilzena makes two attacks: one with its bite and one with its tail.

Bite. Melee Weapon Attack: +15 to hit, reach 15 ft., one target. Hit: 19 (2d10 + 8) piercing damage, and the target must make a DC 20 Constitution saving throw, taking 36 (8d8) poison damage on a failure and half as much on a success.

Tail. Melee Weapon Attack: +15 to hit, reach 20 ft., one target. Hit: 24 (3d10 + 8) bludgeoning damage. Rather than using her Multiattack, Azilzena can instead make only this tail attack and also grapple a Huge or Smaller target on a hit. While grappled (DC 23 to break) in this way, the target is restrained and is dragged along as Azilzena moves. If Azilzena burrows underground while a target is grappled, they must make a DC 15 Dexterity saving throw. On a failure, they take 10 (3d6) bludgeoning damage and become restrained in the sand (DC 10), and on a success, they take half as much damage and are not restrained. Either way, Azilzena's grapple is broken.

Sandblast (Recharge 6). Azilzena exhales sand in a 90-foot line that is 10 feet wide. Each creature in that line must make a DC 24 Dexterity saving throw or take 63 (14d8) bludgeoning damage and be knocked prone. On a successful save, they take half as much damage and are not knocked prone. If a creature is wearing metal armor and fails their saving throw, the AC bonus granted by their armor is permanently reduced by 1. If it is reduced to zero, the armor becomes non-functioning.

Emerge. Azilzena bursts from underneath the ground. All creatures within a 20-foot cube directly above where Azilzena currently is must make a DC 23 Dexterity saving throw. On a failure, they take 33 (6d10) bludgeoning damage, are pushed 10 feet away from Azilzena, and are knocked prone. On a success, a creature takes half as much damage and is not knocked prone. If a creature fails this save by more than 5, they are hurled 10 feet into the air and take fall damage accordingly. Azilzena can only take this attack if they are underground and have sufficient remaining movement to reach the surface. 

Azilzena can take 3 legendary actions, choosing from the options below. Only one legendary action can be used at a time and, unless otherwise stated, only at the end of another creature's turn. It regains expended legendary actions at the start of its turn.

Burrow. Azilzena moves up to its speed underground.

Center. If deafened by any effects, Azilzena clears the condition. Alternatively, it can spend 3 legendary actions to clear a stunned condition.

Emerge (Costs 2 Actions). Azilzena uses Emerge.

Launch (Costs 2 Actions). Azilzena launches herself into the sky up to her flying speed. Opportunity attacks made during this action are made with disadvantage.

Lash (Costs 2 Actions). Azilzena makes a tail or bite attack.

Funnel (Costs 3 Actions). While underground, Azilzena takes in sand and recharges her Sandblast, which can be used on her next turn.