Apatosaurus

Herding. While the Apatosaurus is in a herd of three or more Apatosauruses (Including itself), it gets an extra 10 HP per herd member, has their speed increased by 5 feet, deal 2 extra damage, have advantage on checks made to frighten/targets have disadvantage on saving throws made to avoid being frightened by it, and its Deafening Roar doesn't damage other friendly or neutral sauropods.

Courageous Roar. The Apatosaurus gives any Diplodocuses and Brachiosauruses advantage and +3 on saving throws to resist being frightened. As an action, the Apatosaurus can roar, giving all of its allies +2 to Constitution and rolls made for frightening and resisting the frightened condition for 30 seconds (5 rounds), along with giving them advantage on attack rolls and the first damage die they roll each attack (Roll twice for damage for the same die and take the higher roll).

Trampling Charge. If the Apatosaurus moves at least 15 feet towards a target and hits it with a stomp action, the initial stomp deals two additional damage dice. If it moves at least 10 feet during its turn, it may force two targets within 5 feet of it during any point of the charge to attempt a DC 15 Dexterity saving throw, taking 18 (2d12 + 5) bludgeoning damage on a failed save, or half as much on a success.

Heavyweight. The Apatosaurus cannot be moves by any effect. It can carry up to 30,000 pounds, while still going at full speed. It must eat at least 2,000 pounds of vegetation each day. It cannot swim, only walk at the bottom of water (Speed 25).

Deafening Roar. The Apatosaurus roars very loud enough to shatter glass and unbury light objects. Each creature within 40 feet of it must succeed on a DC 18 Constitution saving throw or take 21 (2d20) thunder damage and be deafened on a failed save, or half as much damage and not deafened on a success. Creatures within 30 feet of it that are medium must succeed on a DC 16 Strength saving throw or be pushed 20 feet away from the Apatosaurus, while small or smaller creatures must succeed on a DC 22 Strength saving throw with disadvantage or be pushed 40 feet away.

Tail Sweep. The Apatosaurus swings its tail in one of its flanks. Each creature on that side of the Apatosaurus' choice within 35 feet must succeed on a DC 18 Dexterity saving throw or take 43 (5d12 + 10) bludgeoning damage on a failed save, or no damage on a success. Large creatures must succeed on a DC 23 Strength saving throw or be knocked prone, while medium or smaller creatures are knocked prone.

Tail Whip. Melee Weapon Attack: +14 to hit, reach 40 ft., 2 targets. Hit: 50 (5d12 + 17) bludgeoning damage and the target must succeed on a DC 27 Strength saving throw or be knocked prone, and pushed back 10 feet on a failure higher than two.

Stomp. The Apatosaurus stomps up to two of its feet, each foot can stomp two 5 ft squares. Creatures on those squares (Or hexes, excluding Apatosauruses) must succeed on a DC 21 Dexterity saving throw or be knocked prone and take 50 (5d12 + 17) bludgeoning damage on a failed save, or half as much and not prone on a success. Creatures within 10 feet of the square (Excluding those in the square and Apatosauruses) must succeed on a DC 17 Strength, 17 Dexterity, or 24 Constitution saving throw or suffer 20 (2d12 + 7) force damage and be knocked prone on a failed save, or 5 (2d4) force damage on a success, without being knocked prone.