Friend of Dog

You have formed a bond with a mastiff; the mastiff understands and obeys your one word commands. The mastiff adds twice your level to its hit points and your proficiency bonus to its attack rolls and save DC of its bite attack. The mastiff has its own initiative and may function as a controlled or independent mount. Additionally, the mastiff gains one of the following abilities of your choice: 

• Bigger Bite. The mastiff’s bite attack inflicts the grappled condition on a hit. This condition ends if the grappled creature uses its action to break the grapple as normal or if the mastiff attacks another creature. The mastiff has advantage on attack rolls against creatures it is grappling.
• Deeper Bond. Your bond with your mastiff is especially powerful. You and your mastiff gain advantage on saving throws against being charmed or frightened. Also, you gain the benefits of the beast bond spell. 
• Blood Hound. Your mastiff gains the benefits of the locate creature spell if it smells an item owned by that creature.

If your mastiff dies, you may spend 10 days of downtime creating a bond with a new mastiff. When you obtain a new mastiff, you may select a different ability to give it.