Cerberus Rex

Primal Instinct. The Cerberus Rex has advantage on saving throws against being charmed.

Frenzied Rage. When one of its heads is damaged, it gains advantage on all attack rolls until the end of its next turn.

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

Multiattack. The Cerberus Rex makes three attacks: one with each of its heads.

Bite. Melee Attack Roll: +17, reach 15 ft. Hit: 36 (4d12 + 10) Piercing damage. If the target is a Large or smaller creature, it is grappled (escape DC 20). Until this grapple ends, the target is restrained, and the Cerberus Rex can't bite another target with the same head.

Tail. Melee Attack Roll: +17, reach 20 ft. Hit: 28 (4d10 + 10) Bludgeoning damage and creatures must succeed on a DC 20 Strength saving throw or be knocked prone.

Roar of Chaos. Once per day, the Cerberus Rex releases a combined roar. Each creature within 60 ft. of it that can hear must succeed on a DC 22 Wisdom saving throw or be frightened until the end of its next turn. If a creature fails the saving throw by 5 or more, it is paralyzed while frightened in this way.

The Cerberus Rex 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 C-Rex regains spent legendary actions at the start of its turn.

Detect. The C-Rex makes a Wisdom (Perception) check.

Thrash. The C-Rex makes a Tail Sweep attack.

Predator's Call (Costs 2 Actions). The C-Rex lets out a deafening roar, inspiring allied beasts within 60 ft. to gain advantage on their next attack roll and 20 temporary hit points.