Very medieval monsters

So im running a campaign heavily based on arthurian legends, beowulf, and the lambton worm as the bbeg.

Im looking for cool monsters to use that are super duper medieval. Especially english, scottish, welsh in origin cause thats sort of the setting.

Im thinking of using a displacer beast because there were often cat monsters, im using a homebrewed glatisant, im using the flail snail, the yale with a giant elk stat block.

Then theres the usual ones like dragons, giants, griffins, trolls

I wanted to know what freaky monsters yall know, homebrew ones very appreciated that have that old medieval feeling or from old bestiaries.