This image, as well as the two acompanying videos, were posted to 4chan's /v/ board on the 4th of November. The image and video details what appear to be unreleased Mii Fighter costumes, more specifically Mii Fighter hats of Mallow from Super Mario RPG as well as a Cacodemon from DOOM.
-= Points =-
+ As most Smash Ultimate modders would attest, it is very difficult to not only make such high quality costumes, but to also get them to run in-game without breaking or looking off.
+ Both of the Mii Fighters in the videos are emoting. This is usually unable to happen with modded Mii Fighter costumes.
+ The Mallow Hat jiggles, meaning that whoever made this hat would've had to have rigged a proper jiggle bone for it, which very few if any Smash mods have done for any game.
+ In spite of many claims to the contrary, nobody thus far has been capable of accurately replicating what is shown in these videos.
~ The hats are very detailed and high quality. While it's entirely possible that this is an indication of them being real, it's also possible, though very unlikely, that dedicated enough fans could accurately replicate this.
~ The timer in the top-right corner is stopped at 2 minutes and 30 seconds. This is consistent with a prior image leak of Ken from Street Fighter, who is coincidentally also in the image and video, in the same pose no less. While they are similar, it's also possible, assuming this is fake, that this was done deliberately by the faker in order to make the images and hats seem more legitimate.
~ Sabi has contacted one of her sources to ask about the hats, and while they believe them to most likely be faked, they could not definitively prove or disprove their legitimacy at this time.