Adult Tyrannosaurus Rex

Keen Smell. The Tyrannosaurus Rex has advantage on Wisdom (Perception) checks that rely on smell.

Poor Sight. The Tyrannosaurus Rex has disadvantage on Wisdom (Perception) checks that rely on sight.

Siege Monster. The Tyrannosaurus Rex deals double damage to objects and structures.

Combative Mount. A trained dinosaur is proficient with light, medium, and heavy armor.

Multiattack. The Tyrannosaurus makes two attacks, one with its bite and one with either its tail swipe or headbutt.

Bite. melee Weapon Attack: +10 to hit,reach 5 ft., one target. Hit: 33 (4d12+7) piercing damage. If the target is a Medium or smaller creature, it is grappled (escape DC 17). Until this grapple ends, the target is restrained, and the tyrannosaurus rex can't bite another target. 

Tail Swipe. Melee Weapon Attack: +10 to hit, reach 10 ft., one target. Hit: 20 (3d8+7) bludgeoning damage. If the target is a creature, it must succeed on a DC 15 Strength saving throw or be knocked prone and pushed 5 ft away. 

Headbutt. Melee Weapon Attack: +10 to hit, reach 5 ft., one target. Hit: 20 (3d8+7) bludgeoning, and if the target is a creature that is large or smaller, it must make a DC 15 Constitution saving throw or become stunned until the end of its next turn.