>>30385836>>30385935570 BST, same as the Four Land Spirit legendaries.
An extremely limited number of them are available in the game. A large amount of the S/M story revolves around the Ultra Beasts. Unique encounter music.
Dunno what else you need to hear my dude. They're fuckin legendaries.
And we can only guess that they are "normal" creatures from their dimension. The amount of actual data on Ultra Space is miniscule, to say that these creatures are "standard-grade" denizens or not is an assumption. It's equally likely that the UBs are exceptionally powerful or very much run-of-the-mill entities.
The only one we can make even small assumptions about in Ultra Space are the Nihilego as that is the only one the player encounters in Ultra Space, where we can see that Nihilegos seem to live in groups, and we see the nature of the fusion abilities which apparently can work on extra-dimensional entities (humans.)
The other UBs simply show up from a Wormhole- so we have no idea how many there are, how powerful they are in Ultra Space or what kind of environment in US that they occur in. All we ever saw was a single hallway's worth of terrain in Ultra Space. A UB such as Guzzlord strikes me as a very powerful in it's home-realm due to it's distinctly evil/final boss appearance and it's endless appetite for matter. It seems unlikely that a great number of infinitely-consuming entities would exist.