Doggo is a decent monster for most decks, and incredibly useful in specialized ones, such as control decks. Its ability is to return a card back to the user's hand, just like Break. Cards sent back to the hand will be reverted to their original state and fully healed.
Doggo is especially useful for the Integrity deck when wanting to make the best use of Abilities - especially Magic. Popular cards to combo with Doggo are Alphys, Snowdrake's Mom, Dogamy, Dogaressa, most legendaries and damage cards like Vulkin.