Anti Titan: Skulldevil

Amphibious nature. The Skulldevil can breath air and water.

Pack Tactics. As long as there is an ally within 30 ft. of the Skulldevil, it gains advantage on attack rolls. 

Titan power. Skulldevils attacks count as magical in order to overcome resistances. 

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

Multiattack . The Skulldevil makes a bite attack, two claw attacks and a tail attack on its turn. It can replace the bite attack with swallow attack. 

Bite Attack. Melee Weapon Attack: +15 to hit, reach 15 ft., 1 target. Hit: 38 (6d10 + 8) piercing damage.

Claw Attack. Melee Weapon Attack: +15 to hit, reach 15 ft., 1 target. Hit: 33 (5d10 + 8) slashing damage.

Tail Attack. Melee Weapon Attack: +15 to hit, reach 40 ft., 1 target. Hit: 38 (6d10 + 8) bludgeoning damage. A creature hit by the tail must make a DC 23 strength check or be knocked 40 ft. away and prone or be grappled by the Skullcrawler (DM chooses).

Swallow Attack. Melee Weapon Attack: +15 to hit, reach 40 ft., 1 target. Hit: a long tongue reaches out and wraps around a large or smaller target, then pulls it into its stomach, where it is restrained and has full cover. A creature starting its turn in the Skullcrawler takes 10d10 acid damage. If the Skullcrawler takes 50 or more damage from inside, it regurgitates all creatures in it. It can have up to 5 large creatures in it. 

The Skulldevil can take 3 legendary actions, choosing from the options below. Only one legendary action option can be used at a time and only at the end of another creature's turn. The Skulldevil regains spent legendary actions at the start of its turn.

Command Skullcrawler (2 Actions). The Skulldevil commands all skullcrawlers to move up to their speed and make a bite or swallow attack.

Bite (1 action). The Skulldevil makes a bite attack.

Swallow (1 action). The Skulldevil makes a swallow attack.