Ancient Chimera

Multiattack. The chimera can use its Frightful Presence then The chimera makes three attacks: one with its bite, one with its horns, and one with its claws. When its fire breath is available, it can use the breath in place of its bite or horns.

Bite. Melee Weapon Attack: +11 to hit, reach 5 ft., one target. Hit: 26 (6d6 + 5) piercing damage. The creature must make a DC 19 strength saving throw or be swallowed. A swallowed creature takes 14 (4d6) acid damage at the start of its turn.

Horns. Melee Weapon Attack: +11 to hit, reach 5 ft., one target. Hit: 24 (3d12 + 5) bludgeoning damage. The creature must make a DC 19 strength saving throw or be pushed back 10 feet and knocked prone.

Claws. Melee Weapon Attack: +11 to hit, reach 5 ft., one target. Hit: 26 (6d6 + 5) slashing damage. The creature must make a DC 19 strength saving throw or be grappled. Two creatures can be grappled at a time. While grappled in this way attacks made against the creature are at advantage. 

Fire Breath (Recharge 5–6). The dragon head exhales fire in a 30-foot cone. Each creature in that area must make a DC 21 Dexterity saving throw, taking 81 (18d8) fire damage on a failed save, or half as much damage on a successful one.

Frightful Presence. Each creature  of the chimeras choice that is within 120 feet and aware of it must succeed on  DC 14 wisdom saving throw or become Frightened for 1 minute. A creature can make the saving throw at the end of each of its turns, ending the effect on itself on a success. If a creature succeeds or the effect ends, it is immune to the chimeras Frightful Presence for 24 hours.

The chimera can take 3 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 chimera regains spent legendary actions at the start of its turn.

• Bite. The chimera makes a bite attack.
• Claws. The chimera makes a claw attack.
• Heat Wave. (cost 2 actions) The chimera releases a massive wave of heat from its core, each creature within 10 feet of it must make a DC 21 Constitution saving throw taking 22 (5d8) On a failure the creature also takes 1 point of exhaustotion.