Trampling Charge. If the zombie moves at least 20ft 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 zombie can make one stomp attack against it using a bonus action.

Gore. Melee Weapon Attack: +7 to hit, reach 5 ft., one target. Hit: 13 (2d8 + 5) piercing damage.

Stomp. Melee Weapon Attack: +7 to hit, reach 5 ft., one prone creature. Hit: 16 (2d10 + 5) bludgeoning damage.