Innate Spellcasting. Zacama Primal Calamity's innate spellcasting ability is Constitution  (spell save DC 20, +12 to hit with spell attacks). It can innately cast the following spells, requiring no components of any kind:

At will: Scorching Ray

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

Multiattack. The tyrannosaurus makes Four attacks: three with its bite and one with its tail. It can't make both attacks against the same target.

Bite. Melee Weapon Attack: +15 to hit, reach 10 ft., one target. Hit: 35 (4d12 + 9) piercing damage. If the target is a Medium or smaller creature, it is grappled (escape DC 23). Until this grapple ends, the target is restrained, and the tyrannosaurus can't bite another target with this head.

Tail. Melee Weapon Attack: +15 to hit, reach 15 ft., one target. Hit: 22 (3d8 + 9) bludgeoning damage.

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

Move. Zacama Primal Calamity may move up to it's speed.

Bite Attack.  Zacama Primal Calamity makes a Bite attack.

Wing Attack (Costs 2 Actions). Zacama Primal Calamity can cast Scorching Ray