Spriggan

Spriggan is a humanoid, forest-dwelling creature.

"Spriggan" in the English version of The Last Wish is a translation of Polish "borowik".

Folklore
Spriggans are legendary creatures known from Cornish faery lore. Spriggans were grotesquely ugly, found at old ruins and barrows guarding buried treasure and generally acting as fairy bodyguards. They were also said to be busy thieves. Though usually small, they had the ability to swell to enormous size (they're sometimes speculated to be the ghosts of the old giants).

Certainly their disposition was poor, and they caused mischief to those who offended them. They sent storms to blight crops, and sometimes stole away mortal children, leaving their ugly changelings in their place.

According to a Russian legend, Baba-Yaga puts the hero in touch with magic creatures (spirits), Lesovik and Borovik, who live under a mushroom and provide the hero with magical gifts which show him the way to reach his goal. In both Polish and Russian, borowik/borovik is also the name of the boletus mushrooms.