Buck

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

Natural Inclination. When YOU (the player) reach 3rd Level; chose one archetype for Buck - Defensive, Offensive, Protective, Aggressive. At 8th Level pick an additional Archetype and gain its associated benefits. 

Offensive: +2 hit and damage on all attacks. 
Defensive: +2 Armour Class and +2 HP per level. 
Protective: As a reaction, the companion may impose disadvantage on an attack against an allied creature within 5ft. 
Aggressive: As a reaction, the companion may move up to 20 ft immediately before attacking. Movement in this way does not provoke opportunity attacks. 

Ability Score Improvement.  When YOU (the player) get an ability score improvement or feat, you may improve one of Buck's stats by 1. 

Adventuring Companion. Buck acts with your initiative and on your turn, unless you both are separated and it makes sense for Buck to act independently. 

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

If the target is a creature medium or smaller, it must succeed on a DC 13 Strength saving throw or be knocked prone.