This is a weird case, but
this thread got me thinking about it
We have profiles for
Brittnay Matthews and
Deandra from The Most Popular Girls In School. This is a hugely popular webseries (well, at least it was a decade ago), with
the first episode having over 11 million views. It also has it's own
wikipedia page.
However, all of the characters, including the two on-site,
all use Barbie dolls (or similar brands) (appearance section) to represent themselves. Usually the dolls are edited, such as having their hair styled or Deandra having a robot arm replacing the doll's typical arm, but at the end of the day they're still Barbie dolls.
Would this fall under fanwork? Using stop-motion Barbie dolls for your characters? Isn't that akin to using the likeness of copyrighted characters? I'm unsure if this would be allowed or not