This entry in Epic Monsters is one I am definitely fond of--a big black dog hailing from the easternmost bit of England, the one and only (or many, as you like) Black Shuck!

Black Shuck is an interesting dog if nothing else. Legends about this canine go back to 1127 and range from it being Satan to a poor fellow’s lonely companion haunting the spot of his death to a terrifying monster that liked to bust into churches to wreck havoc. One thing is for certain: Black Shuck is a great example of localized folklore really taking root. Like the Jersey Devil but much, much older, and also like the Jersey Devil it’s still being spotted here and there.

Design Notes: Like any proper myth many different stories are attributed to or similar to Black Shuck’s and pinning down a definitive one is tricky so I tried to do a catch-all here. I think altogether it’s pretty solid and should make for an interesting encounter or two--toss in a few dire wolves as a screen and let the party spot the cyclops out of the pack, rewarding the first adventurer to do so with a spooky omen about how they might soon perish (utilizing Black Shuck to dole out some plot seeds).

Black Shuck
Large fey, chaotic neutral

Armor Class 16 (natural armor)
Hit Points 76 (8d10+32)
Speed 55 ft.

18 (+4)
17 (+3)
19 (+4)
6 (-2)
18 (+4)
14 (+2)

Skills Athletics +7, Insight +7, Perception +7, Stealth +16
Damage Resistances cold
Condition Immunities frightened
Senses darkvision 90 ft., passive Perception 17
Languages Common; telepathy 100 ft. (images of death omens only)
Challenge 5 (1,800 XP)

Innate Spellcasting. Black Shuck's innate spellcasting ability is Wisdom (spell save DC 15). It can innately cast the following spells, requiring no material components:
Constant: pass without trace
At will: divination (indefinite timespan; death omens only)
3/day: hellish rebuke, hunter’s mark

Keen Hearing and Smell. Black Shuck has advantage on Wisdom (Perception) checks that rely on hearing or smell.

Magic Resistance. Black Shuck has advantage on saving throws against spells and other magical effects.

Terrifying Howl. Black Shuck can use a bonus action to unleash a terrifying howl. Each creature that is within 120 feet of Black Shuck and is able to both see and hear Black Shuck, it must succeed on a DC 15 Wisdom saving throw or become frightened for 1 minute. A creature can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success. If a creature's saving throw is successful or the effect ends for it, the creature is immune to Black Shuck’s Frightful Howl for the next 24 hours.

Multiattack. Black Shuck attacks twice.

Bite. Melee Weapon Attack: +7 to hit, reach 5 ft., one target. Hit: 13 (2d8+4) magical piercing damage. If the target is a creature, it must succeed on a DC 15 Strength saving throw or be knocked prone.