Faithful Dog
Drops from Moonfang. No longer lost or lonely, your faithful companion has decided that by your side is the best place to be. Beast type. You need to have in on the Broken Isles for that character in order to obtain this companion.
The 
Faithful Dog is a companion pet obtained by interacting with Dog on the Tranquil Strand in the Isle of Dorn, requiring you to first establish a history with Dog across Pandaria and Legion Dalaran.
Guide awaiting review
Complete Lost and Lonely Quest
Find the Lost Dog in the Valley of the Four Winds in Pandaria at 42.4, 50.0 and complete his quest, Lost and Lonely. This establishes you as a dog person and is required before Dog will appear for you in subsequent steps.
Bring Dog to Dalaran
Travel to Legion Dalaran and find a 
Pebble on the streets, then visit your Garrison and interact with Dog in the herb garden, and finally find Dog in the Dalaran pet shop. Completing these steps moves Dog to Dalaran and unlocks the next stage.
Skip With a Friend's Garrison
If you have a friend with Dog already present in their Garrison, you can skip the Tillers reputation grind entirely. Obtain the Pebble from the Auction House or Dalaran and give it to your friend, then as group leader hearthstone to your Garrison, have your friend join your Garrison instance via right-clicking their portrait, and have your friend interact with Dog and click the chat bubble to show the Pebble. Your friend's Dog session will count for your character.
Interact With Half-Buried Dog Bowl
Travel to the Tranquil Strand in the Isle of Dorn and find the Half-Buried Dog Bowl at 31.44, 51.31, near the puppy statue. Interacting with it causes Dog to appear with the emote 'Dog is very happy to see you!' — then interact with Dog and select the option that awards you with Faithful Dog.
Tips
Faithful Dog responds to three emotes: /pet, /love, and /kiss.
The Pebble is tradeable and can be purchased from the Auction House if you cannot find one in Dalaran.
Dog will always remain in your Garrison even after completing the Dalaran or Isle of Dorn Dog interactions.
