Mammoth

If the mammoth 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 18 Strength saving throw or be knocked Prone. If the target is Prone, the mammoth can make one stomp attack against it as a bonus action.

Melee Weapon Attack +10 to hit, reach 10 ft., one target. 25 (4d8 + 7) Piercing damage.

Melee Weapon Attack +10 to hit, reach 5 ft., one Prone creature. 29 (4d10 + 7) Bludgeoning damage.