The Fair Folk/WMG

Fey creatures intentionally Disneyfied themselves to be seen as less of a threat to humans.
A couple hundred years ago, the Fey had been happily doing their own thing and messing with humans for centuries, but at one point they realised that the humans keep building themselves sharper swords, tougher armour and big sticks that go bang. Seeing at least some of the devastating weapons to follow, they decided that they'd best avoid retaliation for their 'fun' and being wiped out by changing their image to playful, helpful and cute creatures from Fairyland, and such helpful spirits as the Tooth Fairy and (possibly) Santa Claus.

Seeing things revert somewhat to their old image is probably confusing them a bit, but also at least letting them get a bit nostalgic and go punk rock.
 * If so, then those Jack Frosts are eeeevil.

The Fair Folk (as we think of them) didn't let themselves get Disneyfied, they just went underground and let other races do the PR work for them.
Santa's elves? German brownies. Nobody finds out what happens when they don't get paid because Nicholas/Chris isn't that stupid or cruel, and they have no need or want to go to the television stations of the people who make films about elf strikes being unionized or not effective enough. The Tooth Fairy is all that remains of an anti-legend for beings that steal teeth from the garbage or the ground for sympathetic magic, so the children needed to dispose of them in a way that would make it difficult for the fey to get at them; More recent times have parents outright telling the kids to leave the teeth for the "Tooth Fairy" because they don't ken the power of words and intent. Most of the Fair Folk live underground these days, either literally in the case of more feral earthbound races and those who find abandoned human subways interesting places to set up court or metaphorically in the case of those who stop leaving the pet flap open on their hills to keep the squishy, easily-confused, two-legged toys from getting in as often. The Green Movement, if they've noticed, is simply telling them that all they have to do is wait for us to willingly give up iron... of all kinds. Since we've mostly forgotten about the old ways, it's only a matter of time...
 * If this is at all accurate, then writers like Terry Pratchett whose works contain a fair bit of information on anti-fairy measures have done us all a great service.

Mary Sues ace actually subspecies of The Fair Folk.
Unnaturaly beautiful? Check. Reality Warping powers that bend the canon to their will, and makes sure their stories go in their favor? Check. Perfect in almost every way, and thus completely inhuman due to a lack of flaws and relatable traits? Check. With all this evidence from thousands of fanfics, we can safely guess that Mary Sues are avatars or disguised members of the Fey race, whom insert themselves into a story to toy with mankind (and canon) on a more personal level. Mary Sue Hunter s defeat these creatures by exposing plot holes, bad grammar, and characterization mistakes: similar to how some characters defeat main members of the Fair Folk by using their own words against them.