Im one of the very few people who didnt dislike the Astel rematch. I mean, we are fighting lots of Fallingstar Beasts and full-grown Fallingstar Beasts while also encountering the "malformed stars" (which look exactly like the Astels, just desaturated) hanging from ceilings underground well before we reach the second Astel. Everything points out to those being stages in a creature's lifecycle, so it is pretty obvious that there is more than a single "Astel" and those are just a species or something. I also read somewhere that the correct translation for "Astel" would be "Aster" instead, because Japanese has that thing with switching Ls for Rs and such. "Aster" is the Greek word for "Star" - its where the "Asteroid" word comes from.
So yeah, the lore implication is that the stars in Elden Ring universe are actually Astels - or at least some of them are. So maybe there are billions of them lol. Radahn is said to have kept the stars at bay with gravity magic - this has a completely different meaning when you factor in that those "stars" might be actual living eldritch abominations from the cosmos. There is some cut animation where supposedly Astel would fall from the sky as a meteorite - I'm pretty sure that was initially planned to be Radahn's phase two.
