America-centricism, like headcanon about what Germany and Italy do at Thanksgiving meals. They.... don't? Because they don't have that holiday???
On the other side of the coin, japanese fanart doing the exact same things with specifically japanese tropes.
Also: Ancient clothes. Please somebody draw the Ancients in actual ancient clothes and not randomly draped and tied bedsheets, they drew themselves all the time so you can't blame a lack of references!
Re: Mistakes often made in fanworks
On the other side of the coin, japanese fanart doing the exact same things with specifically japanese tropes.
Also: Ancient clothes. Please somebody draw the Ancients in actual ancient clothes and not randomly draped and tied bedsheets, they drew themselves all the time so you can't blame a lack of references!