But... how can linking fictional worlds be illegal? If you're not plagiarizing another work or violating a trademark?
tl;dr version: The first line of Wakshaani's 9/8 post. Otherwise, read on.
While Old!FASA was still a thing, there was no problem because they owned all the IP involved. The copyrights and trademarks that Old!FASA owned were split up when the company was, presumably along game line... lines. All the Shadowrun IP went to WizKids/FanPro/whoever it was, while the Earthdawn IP bounced around like a superball in a blender. Either holder who uses the other guy's IP without permission is committing an infringement, and is opened up to liability. Which is why we see "legally distinct" references like TWO mentioned; close enough that those in the know get it, but vague enough to prevent legal problems. Of course, if enough of those references get together, it can still cause problems, which is why the folks in charge are careful about it.
Psycho835 got it right, though; anything incorporated into the Shadowrun "canon" prior to the Fall of FASA is Shadowrun IP, not Earthdawn IP, even if there is an incredibly similar bit of IP in the Earthdawn sphere. Each line can take it's copy and run with it, without worry of infringement. However, IP that was created after the split (or not incorporated before the split) runs the risk of infringement if it's used now. An example is dragons: They are a significant piece of each game, and each game can use them in whatever manner it sees fit. The dragon known as Ghostwalker/Icewing can be used by either line, since he was included in both prior to the split. Because they have no ED analog, Lowfyr and Hestaby are off limits in Earthdawn, although ED writers can certainly reference a "male dragon with golden scales" or "an orange female dragon." Referencing a "large, male Great Common Dragon with golden scales who is the brother of Alamais," though not flat-out saying "Lowfyr," is towing the line.
