"The Life and Adventures of Santa Claus" by L. Frank Baum is an adventure I read every year these days, and I was struck by how well some of the descriptions of immortals and their foes would translate to an old-school RPG. So here they are. It's public domain, so read it yourself and write your own monster stats if you disagree, Merry Christmas.
As always, images from the original 1920's book when available, and Rankin & Bass when not.
Not included, though interesting, are the Water Sprites, Sleep Fays, Sound Imps, Wind Demons, and Light Elves.
Ryls
HD 1 AC none Thorns 1
Move Normal Int Low Morale Normal
Wants protect plants, destroy ravagers
Little first cousins to the nymphs, who watch over flowers and plants. They are merry and light-hearted, loving laughter. Their king lives in a distant meadow of gay flowers and luscious fruits.
Each attends a particular type of flower and takes its color for its name and simple garb. (The Yellow Ryl tends the buttercups, for example.)
Gifts: Can bring food, and paint the color of their plant.
Fairies
HD 2 AC as chain (flitting) Golden Wand deflect
Move Fast, flight Int High Morale High
Wants protect mankind, destroy tempters
Dressed in white gauze with rainbow-hued wings and golden wands. They are usually invisible and unknown to mortals. They honor a great queen who protects a magical pool which grants beauty to those who bathe in it.
Golden Wand: Each turn, a fairy can reduce the damage from one attack by 2d4. The attacker takes the same amount as the damage flows back to them (but no more than the attack could have caused). Multiple fairies working together can turn back dragon breath.
Gifts: Can bring cloth and tools.
Knooks
HD 3+1 AC as leather (gnarled) Spear 1d6
Move Normal Int Normal Morale Brave
Wants protect beasts, destroy monstrosities
Old and worn and crooked, anxious and rough, gray beards and scowling brows. They love courage, and are gruff but friendly. Knooks are known by names like "Will" and "Peter". Their great king lives in a distant jungle.
Each band are particular to one woods, but they share a secret language of whistles by which friendship is known. They can teleport creatures between their woods if all parties are willing and friendly.
Stinging Gnats: Once per day a knook can set a swarm of stinging gnats against a foe or recalcitrant beast. The target is blinded and slowed and cannot concentrate. Any area damage destroys the gnats, but damages the target as well. Submersion or strong winds may help.
Gifts: Gather and work (dead) wood and leather from animals that died of old age.
Nymphs
HD 4 AC as chain (wooden flesh) Ash Switch transmute
Move Normal Int Normal Morale High
Wants protect trees, destroy defiers
Tree colored, slender, dressed in oak-leaf green and sandals. They are curious and proud.
Cause Fear: In defense of forests and trees, a nymph can cause 2d4 HD of creatures that can see her to save or flee in fear.
Ash Switch: A creature struck by a nymph's ash switch has its speed reduced by a category. Anything rendered immobile by this effect is transmuted into a clod of dirt.
Gifts: A nymph can seal a dwelling against unwanted incursions.
Awgwas
HD 6 AC as chain (huge, tough) Stone d10
Move Slow Int Average Morale Proud
Wants tempt mortals to mischief, become king
They were of gigantic stature and had coarse, scowling countenances which showed plainly their hatred of all mankind. They possessed no consciences whatever and delighted only in evil deeds.
Their homes were in rocky, mountainous places, from whence they sallied forth to accomplish their wicked purposes.
The one of their number that could think of the most horrible deed for them to do was always elected the King Awgwa, and all the race obeyed his orders.
Limited Invisibility: Invisible to mortals, but not immortals.
Tempt Mortals: Whisper in a mortal's ear to give them advantage on their next check or attack to a petty, cruel, or quarrelsome action.
Bat-Winged Demons from Patalonia
HD 3 AC as leather (flapping) Immiserate d6 morale
Move Normal flight Int Average Morale High
Wants flap through the air spreading misery
Three-Eyed Giants of Tatary
HD 8 AC as plate (gigantic, thick walls of flesh) Slam x3 d8
Move Slow Int Average Morale Brave
Wants fight!
Goozzle-Goblins
HD 1 AC none Sword-Talons d6
Move Normal Int Average Morale High
Wants flay flesh from bones
Wherever a goozle-goblin dies, a thistle will grow.