Legendary Resistance (3/Day). If the Black dog fails a saving throw, it can choose to succeed instead. Turn Resistance. The black dog has advantage on saving throws against any effect that turns undead.
Bite. Melee Weapon Attack: +9 to hit, reach 10 ft., one target. Hit: (3d8 + 9) piercing damage plus (8d6) soul damage. Multiattack.The black dog makes two attacks with its chains. Chain.Melee Weapon Attack: +6 to hit, reach 20 ft., one target. Hit: (4d6 + 6) slashing damage. The target is grappled (escape DC 25) if the black dog isn't already grappling a creature. Until this grapple ends, the target is restrained and takes (3d8) soul damage at the start of each of its turns. Animate Chains. Up to four chains the black dog can see within 80 feet of it magically sprout Bright Blue Soul fire and animate under the black dog's control, provided that the chains aren't being worn or carried. Each animated chain is an object with AC 22, 50 hit points, resistance to piercing damage, and immunity to psychic and thunder damage. When the Black dog uses Multiattack on its turn, it can use each animated chain to make one additional chain attack. An animated chain can grapple one creature of its own but can't make attacks while grappling. An animated chain reverts to its inanimate state if reduced to 0 hit points or if the black dog is incapacitated or dies.
The black dog can take 3 legendary actions, choosing from the options below. Only one legendary action option can be used at a time and only at the end of another creature's turn. The black dog regains spent legendary actions at the start of its turn. Blink, the black dog blinks into the ethereal plane and reappears somewhere within the 10 km of its graveyard. Bite (cost 1 action), the black dog makes a bite attack Multiattack (cost 2 actions).The black dog makes two attacks with its chains and grapples anyone captured in them.
if the black dog is destroyed or killed it will reappear within 1d20 days
the black dog inhabits and protects a 10 kilometer graveyard
fewer ghouls and grave robbing
the black dog is a huge beast covered in blue spectral flames that forever burn away at its soul, it has ethereal chains binding it to the graveyard to keep it from leaving, its eyes are pure white representing its blindness to anything but that which would defile its territory. it is said that a black dog will keep even the meanest devil away.
Graveyard, the black dog is the first creature buried in a graveyard and the act forever dooms it to be the protector of the place. a black dog can cover about 10 KM of graveyard ground, any more and ghouls start overwhelming it with there spawn rates, be careful when mixing two graveyards together, black dogs are rather territorial and if they do not get along the first night separate the graveyards for they never will.