Keen Hearing and Smell. The wolf has advantage on Wisdom (Perception) checks that rely on hearing or smell.

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

Shadow Health. The hound appears with a number of temporary hit points equal to half the sorcerer level of the person who summoned it.

Shadow Stride.  The hound can move through other creatures and objects as if they were difficult terrain. The hound takes 5 force damage if it ends its turn inside an object.

Relentless Pursuit. At the start of its turn, the hound automatically knows its target’s location. If the target was hidden, it is no longer hidden from the hound.

Shadowy Summons. The hound appears in an unoccupied space of your choice within 30 feet of the target. Roll initiative for the hound. On its turn, it can move only toward its target by the most direct route, and it can use its action only to attack its target. The hound can make opportunity attacks, but only against its target. Additionally, while the hound is within 5 feet of the target, the target has disadvantage on saving throws against any spell you cast. The hound disappears if it is reduced to 0 hit points, if its target is reduced to 0 hit points, or after 5 minutes.

Bite. Melee Weapon Attack: +5 to hit, reach 5 ft., one target. Hit: 10 (2d6 + 3) piercing damage. If the target is a creature, it must succeed on a DC 13 Strength saving throw or be knocked prone.