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

Scent Tracker. Yumi has advantage on Wisdom (Survival) check to track a creature based on smell.

Life Oath (must be earned). Unique bond that allows for telepathic communication (no words, simple things like emotions and feelings).

Bite. Mele Weapon Attack: +4 to hit, reach 5ft., one target. Hit: 5 (1d6 + 3) piercing damage.

Blink Shadow (Recharge 4-6). Yumi magically hides in the nearest shadow and can teleport, along with any equipment it is wearing or carrying, up to 40ft. to another space as long as there are shadows. Before or after teleporting, Yumi can make one bite attack. 

Go Fetch. Reaction triggered by command from character with bond (action must be spent). Yumi imposes disadvantage on the attack roll of a creature within 40ft of it whose target isn't Yumi by Shadow Blinking into the enemy shadow and biting and pulling on his ankle leaving the character unable to move for 1 turn. Yumi must be able to see, hear or smell the attacker.