The Spanish mythlogy based in folklore is very, very, very rich, specially about the feys. The Spanish Reconquest is a very interesting age. The conflicts in the Spanish XIX century also can be used as source of inspiration.
Even there is a Spanish TTRPG: "Aquelarre" based in Spanish mythology. And this is still be published.
en.wikipedia.org
mythus.fandom.com
Read about Spanish mythology, mythical creatures, legends and folklore - richly interesting stories from various historic regions.
travelnhistory.com
en.wikipedia.org
The legends written by Gustavo Adolfo Bequer have got a special Spanish touch for the gothic horror you are used.
From Reddit:
The dip, a three legged "vampiric" dog who sucks the blood of drunkards and other easy prey in the streets at night.
A cuelebre is a race of giant snake, with strange magical powers that mostly stays alone with some treasure in streams and rivers until its big enough to go to the sea bottom and stay there forever, sometimes they attacks locals and kills people, so once San Juan killed one of them and since the Cuelebres powers wane at the summer solstice (noche de San Juan).
The meigas are basically how you call witches in Galicia.
The Busgosu is a goatman that causes tisis (horrible actual illnes) to hunters, woodchopper and other people in the forests.
The Nuberu is a tall old men, with basically the powers of storm from x-men controlling all the weather, is probably a celtic demigod or minor god that eneded as a myth after the romans.
A guaxa is a decrepit old lady, with owl eyes and a single teeth, she sneaks into houses with the objective of biting someone with her single teeth spreading an illnes.
The pesanta is a big black dog with heavy iron paws that sneaks into houses at night and puts his paws in your chest leaving you unable to move and barely breathin. Basically a mythological explanation for nightly terrors.
The Hesengu was a devil in dragon form who basically did dragon things but also making people go crazy when under his shadow.
The trasgu is basically a goblin (the original ones , not the orcs ones).
The lavandeiras are spirits of women who died giving birth or similar tragic deads and appear to people while washing clothes at night under the moon, and ask you for your help. To avoid misfortune you have to both help them and when the lavadeiras twists their clothes to pull out the water you must do the same in the contrary direction.
The ojoncanu is an evil rehead giant.
Down in the post people talked about the santa compaña and the ghost of count Arnau, the genti di muerti.
We also have dryads and nymphs but called alojas.