Keen Hearing and Smell. The Gaunt has advantage on Wisdom (Perception) checks that rely on hearing or smell.
Pack Tactics. The Gaunt has advantage on an attack roll against a creature if the Gaunt's rider is mounted and within 5 feet of the creature and the rider isn't incapacitated.
Chill of the Grave. Any living being foolish enough to mount a Gaunt must make a DC (CON+PB) Con saving throw if the Gaunt isn't incapacitated. If the saving throw fails by 5 or more, the creature is instantly petrified. Otherwise, a creature that fails the save begins to turn to ice and is restrained. The restrained creature must repeat the saving throw at the end of its next turn, becoming petrified on a failure or ending the effect on a success. The petrification lasts until the creature is freed by someone pulling them off.
Silent Dead. The Gaunt has advantage on Dexterity (Stealth) checks that rely on listening. Gaunts make no sound and if traveling with their rider, they can move stealthily at a normal pace.
Undying Bond. You can add your proficiency bonus to any ability check or saving throw that the Gaunt makes.
Unusual Nature. The Gaunt doesn’t require air, food, drink, or sleep.