SRD
Keen Hearing and Smell. The Small Terrier has Advantage on Wisdom (Perception) checks that rely on hearing or smell.
Scent Tracking. If the Retriever has a scent of a item or person they can track it for up to 1 mile away, and follow its path within 12 hours.
Rutting. A Small Terrier can attack a creature that underground within range of it, and is able to easily squeeze into small spaces to follow a target.
Bite. Melee Weapon Attack: +0 to hit, reach 5 ft, one target. Hit: 1-2-4 1d4 Piercing damage.