Cycle. The titanoth rex emits an aura with a 120 ft. radius that encourages magic surges. When rolling for wild magic, crystal rolls, or similar affect that would result in a magic surge, if the roll does not result in a magic surge, roll again. 

Siege Monster. The titanoth rex deals double damage to objects and structures.

Trample. If the titanoth rex reduces a creatures HP to 0 the titanoth rex may make an attack as a bonus action.

Multiattack. It then makes five attacks: one with its bite, two with its claws, one with its horns, and one with its tail. It can use its Swallow instead of its bite.

Bite. Melee Weapon Attack: +17 to hit, reach 10 ft., one target. Hit: 36 (4d12 + 10) piercing damage. If the target is a creature, it is grappled (escape DC 17). Until this grapple ends, the target is restrained, and the titanoth rex can't bite another target.

Claw. Melee Weapon Attack: +17 to hit, reach 15ft., one target. Hit: 28 (4d8 + 10) slashing damage.

Horns. Melee Weapon Attack: +17 to hit, reach 10ft., one target. Hit: 32 (4d10 + 10) bludgeoning damage.

Tail. Melee Weapon Attack: +17 to hit, reach 20ft., one target. Hit: 24 (4d6 + 10) bludgeoning damage. If the target is a creature, it must succeed on a DC 20 Strength saving throw or be knocked prone.

Swallow. The titanoth rex makes one bite attack against a Large or smaller creature it is grappling. If the attack hits, the target takes the bite's damage, the target is swallowed, and the grapple ends. While swallowed, the creature is blinded and restrained, it has total cover against attacks and other effects outside the titanoth rex, and it takes 56 (16d6) acid damage at the start of each of the titanoth rex's turns.

Trampe Cycle.  If a crystal roll results in a spell cycle round, the titanoth rex can target a creature within 60 ft. of it. The targeted creature gains titanoth rex's trample ability.