Cave Triceratops

Keen Smell. The cave triceratops has advantage on Wisdom (Perception) checks that rely on smell.

Sunlight Sensitivity. While in sunlight, the cave triceratops has disadvantage on Attack rolls, as well as on Wisdom (Perception) checks that rely on sight.

Trampling Charge. If the cave triceratops moves at least 20 feet straight toward a creature and then hits it with a gore attack on the same turn, that target must succeed on a DC 13 Strength saving throw or be knocked prone. If the target is prone, the cave triceratops can make one stomp attack against it as a bonus action.

Variant: Cave Dinosaur Mutations. As a result of the specialized breeding programs of the Yuan-Ti, some cave dinosaurs differ from their kin and display odd mutations. While these mutations are not common, and even less so in populations in locations remote from the influences of the Yuan-Ti, the DM may roll a d100 before an encounter to determine what mutation appears:

01-10: The legs of this cave dinosaur are particularly large and muscular. The cave dinosaur gains an additional 10 ft. of movement and is unaffected by non-magical difficult terrain.
11-12: Remnants of the profane magic that transformed them still linger in the cave dinosaur’s scales, causing them to glimmer in the pale light. The cave dinosaur has advantage on Saving Throws against all Spells and magical Effects.
21-30: Like a chameleon, the scales of this cave dinosaur change color so as to blend in with their surroundings. The cave dinosaur has advantage on all Dexterity (Stealth) rolls it makes.
31-40: Globules of acid drip from this cave dinosaur’s mouth. The cave dinosaur is able to spit acid as per the spell Acid Splash, using Dexterity as the Spellcasting Ability.
41-50: Poison courses throughout the body of this cave dinosaur, and seeps forth from between every scale. All melee attacks the cave dinosaur performs deal an additional 1d6 worth of poison damage.
51-60: Barbels dangle from the sides of this cave dinosaur’s head, writhing gently in the dark. The cave dinosaur has 10 ft. of blindsight in addition to its other senses.
61-65: This particular cave dinosaur seems especially large and bulky. The cave dinosaur has advantage on all of its Strength checks against creatures of size Large or smaller, and it counts as one size larger when it comes to weight it can push or lift.
66-70: This particular cave dinosaur seems healthy and well-nourished. The cave dinosaur has advantage on all of its Constitution checks and is resistant to poison damage. 
71-75: This particular cave dinosaur seems lithe and dextrous. The cave dinosaur is able to take the Disengage action as a bonus action on each of its turns. 
76-80: Yuan-Ti rituals have enhanced the resistances of this creature. The cave dinosaur is resistant to lightning and fire damage.
81-85: Yuan-Ti rituals have enhanced the resistances of this creature. The cave dinosaur is resistant to cold and lightning damage.
86-90: Yuan-Ti rituals have enhanced the resistances of this creature. The cave dinosaur is resistant to fire and cold damage.
91-100: This cave dinosaur has grown a pair of large, almost draconic-looking wings upon its back. The cave dinosaur has a fly speed of 30 ft. in addition to its normal forms of movement.

Gore. Melee Weapon Attack: +8 to hit, reach 5 ft., one target. Hit: 18 (3d8 + 5) piercing damage.

Stomp. Melee Weapon Attack: +8 to hit, reach 5 ft., one prone creature. Hit: 16 (2d10 + 5) bludgeoning damage.