Trampling Charge. If the terastodon 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 terastodon can make one stomp attack against it as a bonus action.
Gore. Melee Weapon Attack: +10 to hit, reach 10 ft., one target. Hit:25 (4d8 + 7) piercing damage.
Stomp. Melee Weapon Attack: +10 to hit, reach 5 ft., one prone creature. Hit:29 (4d10 + 7) bludgeoning damage.
A terastodon is an enormous elephant (use the mammoth statistics) with four tusks and armored hide. A bony plate on its head, sharply pointed on the edges, extends back to protect its neck.