The mythical creatures of Ireland and England are pretty famous. Leprechauns are almost cliché at this point (use Gancanagh instead, is my advice) and any depiction of giants that aren’t Norse are usually based on old English giant myths.
I really recommend Jack the Giant Killer, it’s very OSR.
The other British mythologies don’t get as much coverage, I don’t think. Welsh, Cornish, Manx and Orcadian monsters rarely feature in media (with the possible exception of the Orcadian Nuckelavee, which is a really good monster.)
However, the one I know most about that gets ignored is Scots mythology. And let me tell you, Scots monsters are gameable.
Beithir - The Scots Dragon. Its name variously means ‘thunderbolt’ or ‘serpent’. In fairness, this is cheating, because it’s already in D&D as the ‘Behir’ of the Monster Manual. The ‘giant snake-dragon’ angle is played up pretty well, but one story that’s missed out is the Beithir’s ability to mind-control anyone they wind around the neck of. The mythical Beithir can disguise itself as a tunic, or perhaps a necklace or torc. Perhaps the local laird is suddenly acting cruel and erratic after a man from the hills gifted him a new cloak?
Another quality of the Beithir is reviving itself from death unless it’s decapitated and the head burned. They can’t breathe fire or fly, but they’re physically powerful and aquatic. Supposedly the last beithir was killed in Islay, in 1900, with cannons and spikes.
Ghillie Dubh (Gilly Du) – A solitary fairy found in a birch forest by Loch a Druing. A friendly, helpful male Dryad, basically, who lives a harmless life in a forest and helps lost travellers. A wholesome social encounter for your party. The ‘real’ Ghillie Dubh was supposedly driven away forever when the local laird sent a party to hunt and capture him.
Labh-allan (Lavellan) – A wee harmless looking water-rodent, usually found dwelling in deep pools or wells. Regarded as a kind of shrew or vole, but one that was ridiculously, hilariously poisonous, to the point of killing cattle at 100 paces. Supposedly found mostly in Caithness, right up in the north.
Kelpie – A shapeshifting aquatic horse-creature, well known for two primary powers: the ability to take a human form, and the ability to make their skin adhesive. The classic story I always heard was of a young fisher or similar seeing a wild horse on the edge of a loch, trying to ride it, becoming stuck, and getting dragged screaming to their doom. A Kelpie would likely have a hell of a hoard of stolen treasures down among the slimy wrack of the loch – steal or negotiate, either works.
Selkie – Shapeshifting seals who ‘step out’ of their skin and become humans. Orcadian myths suggest their seal forms were much bigger than ordinary seals. Anyone who holds a selkie’s seal skin can control them, but they’re long-lived magical shape-shifters. This is a GLOG class waiting to happen, and, in my opinion, the replacement for playable elves in a theoretical Scottish myth campaign.
Blue Men of the Minch – Merfolk native to the Minch, the cold, squally body of water between Scotland and the Hebridean islands (where we used to go for family holidays when I was a wain.) If they catch up to your ship, their leader calls out two lines of poetry and demands you complete the verse.
Blue Chief: Man of the black cap what do you say
As your proud ship cleaves the brine?
Skipper: My speedy ship takes the shortest way
And I'll follow you line by line
Blue Chief: My men are eager, my men are ready
To drag you below the waves
Skipper: My ship is speedy, my ship is steady
If it sank, it would wreck your caves.
If you don’t, or do so badly, they sink your ship. The idea of Blue Men trying this on the modern metal-hulled CalMac car ferries is humourous. You have my express permission to update the above to a rap battle, if you want.
One interpretation of the Blue Men is as dolphin-folk, in effect merfolk with delphinid qualities as opposed to fishlike. They’re also called ‘storm kelpies’ on occasion.
Wulver – Shetland isn’t part of Scotland proper; they have many of their own customs and creatures (such as the Up Helly Aa fire-festival). One such creature is the Wulver, a benevolent werewolf who catches and provides fish to poor families (likely an excuse for anonymous charity in the community.) Wulvers could do a good job of faking out your player’s expectations for lycanthropes, or replacing dwarves as your cheery hirsute folk.
Bodach and Cailleach – Old Bastard and Hag, translated roughly. Basically, the bogeyman and a witch, but also a cranky old married couple. Bodach is a foul, rude, scowling old lout, who comes down the chimney to kidnap rude children. Cailleach is from the same mythological origin as the Annis and Gwyllion, which became the D&D Hag. Cailleach specifically became the Bheur Hag.
Special mention to the Scots Gaelic term for owl, ‘Cailleach-oidhche’, literally meaning ‘Night Hag’, and the Bodach Glas, the Dark Grey Man, who supposedly foretells death. If I was using Bodach and Cailleach, I’d play up their nimbleness and owlish qualities respectively. Probably NPCs for the party to bargain with.
Sluagh (Slooa) – Probably of similar mythological origins to the Wild Hunt or Fairy Host of Germanic myth. A bunch of souls of the unforgiven dead, who fly along the sky in a crescent shape and pick people up, carrying them miles away, or to another island. Sometimes said to rescue people from dangerous crags, but that seems the exception rather than the rule.
Glaistig – A kind of vampire, a beautiful woman with the legs of a goat. Regarded as a patron of cattle drivers, possessed of an enthralling voice. Recognisable similarities to Scandinavian huldra and Greek sirens alike.
Benandonner – When I was 11, I went on a trip to Ireland to visit the town some ancestors had lived in. The town itself was boring, but the trip was great. The highlight was the visit to the Giant’s Causeway, where I heard about the Scottish Giant Benandonner, who was tricked and made a fool of by Fionn MacCumhaill of Irish myth (Finn MacCool). As you might expect, I preferred Benandonner.
Described as a giant among giants, ridiculously tall and incredibly gullible. To give it a D&D link, the Causeway was called ‘The Stepping Stones of the Fomorians’, apparently, so there you have how I’d interpret Benandonner. A really fucking big, dense Fomorian, with a fiery red beard thick as a tangle of ropes and a sword fifty paces long.
Brunaidh (Brownie) – Also called Grugachs, which Gygax has tricked the world into thinking means ‘Elf’. They’re basically your standard house-spirit, like the Bwbach or the Hob. They help around the house dressed in rags, when the humans are asleep, in exchange for cream or porridge. They leave if you give them clothing (Rowling got it from here) or if you try and baptise them. They definitely come across as uptight wee pricks in the myths, since half the stories are about all the specific ways you can piss them off.
Trow – Another Shetlander creature, shy, small, nocturnal and ugly creatures, usually unseen but blamed for missing items and small thefts. It was terrible luck to see a trow, but a good omen to hear one speaking. Another Scots creature that became a weird elf thanks to Gygax – I think replacing D&D Drow with Shetland Trows would be very interesting. Turns out the primary inhabitants of the Underdark are 2 and a half feet tall and look absolutely boufin.
Redcaps – Have found their way into D&D just fine. Originate from the blood-soaked wilds of the Scottish borders region, and often associated with the ‘reivers’ and ‘moss-troopers’, semi-nomadic brigands with allegiance to neither nation. The cap soaked in blood thing is translated pretty much right from the myths.
Nessie – You might have heard of Nessie. Probably the most famous Scottish monster, a water-creature (usually depicted as a plesiosaur these days) that cropped up as a cryptid in 1933. Would be hard to make work in a game, since she’s so commercialised, but I’m planning to have her in that Esoteric Enterprises game set in Glasgow I’ll never run. Another running gag I use is paranormally knowledgeable characters being regretful for some kind of undescribed incident involving Nessie. ‘Poor Nessie.’
Funnily enough: Nae Elves.
Or at least not D&D Elves. The Fair Folk are the villains in most Celtic myths. Do not fuck with the Good Gentlemen of the Hills. You can’t just play one and go running around. They’re careless, hungry, pagan godlings. Terry Pratchett’s Elves are the best example, I think. The ‘Fuath’, which I think map best to Scottish elves, are basically Deep Ones, aquatic creatures that interbreed with humans.
King James VI regarded elves as a possible policy problem for Scotland, and most ballads (Tam Lin, the Elf-Knight, and The Queen of Elfland’s Nourice, for example) have the elves as sociopathic kidnappers. They’re a random encounter, and a bad one, not something a PC can be.
As you may notice, a hell of a lot of these creatures are associated with streams and water, and if not that, then bad weather. Which should probably say a lot about Scotland’s primary qualities.