Adolescent Deviljho

Aggressive. As a bonus action the deviljho can move up to half its speed towards a creature it can see.

Multiattack. The deviljho makes two attacks, one with its tail and one with its bite.

Bite. Melee Weapon Attack: +11 to hit, reach 10 ft., one target. Hit: 32 (4d12 + 6) piercing damage plus 7 (2d6) acid damage. Any nonmagical piece of armor worn by a creature hit by this attack suffers a permanent -1 penalty to its AC. Armor reduced to 10 AC or a shield reduced to a +0 bonus is permanently destroyed. If the target is Medium or smaller it is grappled (escape DC 19). While grappled in this way the target's armor continues to degrade at the beginning of each of the deviljho's turns, and the target takes 7 (2d6) acid damage. Until this grapple ends the target is restrained, and the deviljho cannot bit another target.

Swallow. The deviljho makes one bite attack against creature it is grappling. If the attack hits, that creature takes the bite's damage and is swallowed, and the grapple ends. While swallowed, the creature is blinded and restrained, it has total cover against attacks and other effects outside the deviljho, and it takes 33 (10d6) acid damage at the start of each of the deviljho's turns. Armor continues to degrade in this environment as well; nonmagical weapons now degrade as well, suffering a cumulative permanent -1 penalty to attack rolls made with them. If a weapon reaches a -5 it is permanently destroyed.
If the deviljho takes 30 damage or more on a single turn from a creature inside it, the deviljho must succeed on a DC 18 Constitution saving throw at the end of that turn or regurgitate all swallowed creatures, which fall prone in a space within 10 feet of the deviljho. If the deviljho dies, a swallowed creature is no longer restrained by it and can escape from the corpse using 15 feet of movement, exiting prone.

Tail. Melee Weapon Attack: +11 to hit, reach 15 ft., one target. Hit: 22 (3d10 + 6) bludgeoning damage. The target must make a DC 19 Strength saving throw or be knocked prone.

Dragon Breath (Recharge 6). The deviljho rears back, black smoke seeping from its maw. It exhales in a powerful 30 foot cone of black fog, interlaced with jagged bolts of red energy. Creatures in the are must make a DC 19 Dexterity saving throw or take 21 (6d6) points of necrotic damage plus 21 (6d6) points of lightning damage.

The deviljho can take 2 legendary actions, choosing from the options below. Only one legendary action can be used at a time and only at the end of another creature's turn. The deviljho regains spent legendary actions at the start of its turn.

Move. The deviljho moves up to half its speed.

Tail. The deviljho makes one tail attack.

Bite (Costs 2 Actions). The deviljho makes one bite attack.

The deviljho's mythic trait goes into effect as soon as it is reduced to half of its hit points; even if the deviljho regains hit points that put it above the halfway point it remains enraged. The rage ends after one hour. While enraged the deviljho is resistant to all damage and all of its attacks are considered reckless (as in the barbarian feature). While enraged the deviljho can use the following options as legendary actions.

Stomp. The deviljho slams its foot into the ground, causing tremors in a 10 foot radius of it. Creatures in the are must make a DC 19 Strength saving throw or be knocked prone.