The Disc is hardly a world of originality. That's not to say that it's a dull, uninteresting, normal, or mediocre sort of world; far from it. It is more that its interestingness comes from being a sort of cosmic melange[1] of everything its gods took a shine to that hadn't been securely bolted down.
[1]: which is not, contrary to popular belief, the name of a sort of rusty orange color
That's the sort of behavior that gives you a disc floating through space balanced across the backs of four primordial pachyderms who circle, in turn, atop the shell of a truly astronomical turtle.
Sometimes, a god or few would take inspiration from a passing wonder on a nearby world[2], and cobble together something similar to it. That's how the first swamp dragons[3] happened.
[2]: The view atop Mt. Dunmanifestin, at the Hub of the Disc, is quite lovely.
[3]: Adorably disgusting creatures, rather like reptilian pugs[4] in a number of ways. They have the unique feature of being able to rearrange their own innards on-the-fly to try to turn things they eat into a fiery breath weapon. They are biological alchemical plants, with all of the fumes and explosions that implies.
[4]: Except that their host of alarming medical issues can be blamed more on the gods than on man.
Other times, though, the gods just lazily copy something wholesale without even bothering to file the serial numbers off.
The gods were feeling quite lazy when Equestria flew by…
Thankfully, the great melting pot of the City of Ankh-Morpork exists to accept such fruits of the gods’ caprice, whether they like it or not.