A killer chimeric dog seems pretty appropriate for an Elden Ring boss battle.
A fun detail with the Burial Tree Watchdog is that you can spot identical -- but harmless -- statues in several of the game's catacombs, something that doesn't bode well for the future.
For the actual boss, however, head to the Stormfoot Catacombs. Progress through until the corridor brings you to a room that has already been crossed. Go down a landing and activate the level you'll find, which opens the door to the boss.
The Watchdog can then be found not far from the entrance. You'll have to deal with some annoying gargoyles along the way.
Combat
For melee classes, summoning the Noble Sorcerer is a good idea. Its ranged spells will offer valuable support throughout the fight. The Lone Wolves are likely to die quite quickly, even if they have the potential to deal more damage.
While the battle isn't overly difficult, it can be quite frustrating. You'll likely fail a couple of times as you get used to the Watchdog's erratic attacks. It's prone to thrusting with its Greatsword when you approach, and you should beware of its sweep attack.
When the Watchdog begins to breathe fire, you can either rotate with it to stay within melee range, or simply back away.
Towards the end of the fight, the Watchdog will begin using a plunge attack. Make sure you move away from this, as it hits in a wide area. If you're quick enough you can get some free hits in after impact.
Generally speaking, it's a battle you'll want to play safely, dodging in and out for a few hits before backing off. It's even easier for casters or ranged classes -- just keep your distance.
Rewards
Victory will reward you with 800 Runes, as well as the fantastic Ash of War: Glintsword Arch.
This grants the Glintsword Arch skill for thrusting weapons, and adds the Magic affinity for increased Magic Damage and Intelligence scaling. It will reduce Strength and Dexterity scaling though, and reduce Base Damage.
