Charge. If the Zergling moves at least 20ft straight towards a target and hits with it's bite attack on the same turn, the target takes an extra 3 (1D6) piercing damage. If the target is medium or smaller they must succeed on a DC 10 Strength saving throw or be knocked prone.

Keen smell. The Zergling has advantage on Wisdom (Perception) checks that rely on smell.

Ambusher. The Zergling has advantage on attack rolls against creatures that haven't acted yet or that it was hidden from.

 Pack tactics. The Zergling has advantage on an attack roll against a creature if at least one of the Zergling's allies is within 5 feet of the creature and the ally isn't incapacitated.

Multiattack. The Zergling makes two attacks: one with it's bite and one with its claw

Bite. Melee Weapon Attack: +4 to hit, reach 5 ft., one target. Hit: 5 (1d6 + 2) piercing damage. 

Claws. Melee Weapon Attack: +4 to hit, reach 5 ft., one target. Hit: 7 (2d4 + 2) piercing damage.