Shantaks

Like Byakhee, Shantaks are typically treated as mounts. Unlike the Byakhee, however, Shantaks are not very intelligent, so are more suited to the role. Also like Byakhee, Shantaks can fly through space. They are described as being larger than an elephant with a head like a horse's. Despite also being referred to as a "Shantak-bird", they have scales instead of feathers.

In the RPG...

Shantaks are animalistic and decently tough. Their attack does an average of 17 damage, so could easily take out an Investigator in a single hit, and they have 9-point armour, which means most guns won't hurt them. It should be noted that the 7e Malleus Monstrorum has slowed the Shantaks down considerably. Whereas the old edition had a flight Move of 30, the new one has them at 18—which is still a swift 450 mph. Surprisingly, none of their other stats have been changed. A new bite attack has been added, however, which requires an opposed STR roll to escape from. Shantak's have 170 STR though, so an average human only has a 10% chance of breaking free.

In a video game...

With Shantaks being difficult to kill, but not impossible, they would work well as a boss. As I mentioned with the Byakhee, I would be inclined to leave their rideability out however.

In a film...

Most art depicts Shantaks as dragon-like, so I think they'd need a unique appearance to be worth including in a film.