Trampling Charge. If the elephant moves at least 20 ft. straight toward a creature and then hits it with a gore attack on the same turn, that target must succeed on a DC 12 Strength saving throw or be knocked prone. If the target is prone, the elephant can make one stomp attack against it as a bonus action.
Actions
Gore. Melee Weapon Attack: +8 to hit, reach 5 ft., one target. Hit: 19 (3d8 + 6) piercing damage.
Stomp. Melee Weapon Attack: +8 to hit, reach 5 ft., one prone creature. Hit: 22 (3d10 + 6) bludgeoning damage.