Carnifex

Tunneller. The carnifex can burrow through solid rock at half its burrowing speed and leaves a 10-foot diameter hole in its wake.

Keen Smell. The carnifex has an advantage on Wisdom (perception) checks on checks that rely on smell.

Multiattack. The carnifex can use its Frightening Presence. It then makes three attacks: 0ne with its Crushing Claws and two with its Talons

Bite. Melee Weapon Attack: +7, reach 5ft; one target: Hit 10 (1d10 + 5) piercing damage.

Talon. Melee Weapon Attack: +7, reach 10ft; one target. Hit: 12 (2d6+5) slashing damage.

Crushing claw. Melee Weapon Attack: +7, reach 5ft; one target. Hit 14 (2d8+5) bludgeoning damage.

If the target is a large or smaller creature, the carnifex attempts to grapple the target DC 16. On success the target if not grappled, fail the target is grappled and at the start of the carnifexs' turn, it can use its action to crush the target dealing 2d8 bludgeoning damage.

Frightening Presence.  Each creature of the Carnifex's choice that is within 120 feet of the Carnifex and aware of it must succeed on a DC 16 Wisdom saving throw or become Frightened for 1 minute. A creature can repeat the saving throw at the end of each of its turns, ending the effect on itself on success. If a creature's saving throw is successful or the effect ends for it, the creature is immune to the Carnifex's Frightful Presence for the next 24 hours.

Clubbed Tail (recharge 5-6). Each creature with 10-feet of the carnifex must make a DC 16 Dexterity saving throw. On a fail, a target takes 18 (2d12 + 5) bludgeoning damage and is pushed directly back 20 feet away from the carnifex and is knocked prone. If a thrown target strikes an object, such as a wall or floor, the target takes 3 (1d6) bludgeoning damage for every 10 feet it was thrown. If the target is thrown at another creature, that creature must succeed on a DC 16 Dexterity saving throw or take the same damage and be knocked prone.

If the saving throw is successful, the target takes half the bludgeoning damage and isn't flung away or knocked prone. 

The carnifex 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 carnifex regains spent legendary actions at the start of its turn.

Bite. The Carnifex makes one Bite attack against one creature that it has grappled

Move. The Carnifex can move up to its walking speed.

Clubbed Tail (costs 2 actions). The Carnifex makes an attack with its Clubbed Tail