nah, just 1 of them. You should get it as soon as you beat it too, so you don't even need to bother to finish the map unless you want to. I do think you need to finish the map if you want it registered in the Dark Record, though.

I just beat one but I didn't receive the achievement, could it be a bug?

Did you make sure to pass the bill and that they indeed had max stats (40 mil)? Also, were you by any chance offline? Some games only reward you with achievements if you're online (some you can unlock while offline, but they'll only register when you go online), I don't remember how this one keeps track of them.

I realized that I beat the bosses in different save files and they were not recorded in my dark record, now the question is, do I have to find Prinny Baal again in the item world to unlock pringer x?

Couldn't you just load the one with the most progress? Otherwise, yeah, you'll have to find Prinny Baal again for Pringer X Unleashed

Also, when you said achievements, you meant the steam one, right? Or just the entry from the Dark Record? If it's the former, it doesn't matter which save file you used, it should've popped up as soon as you defeated the first one (and, as mentioned, possibly playing online)

Yes, the steam ones, I think it matters that it is in the dark records because I have already beaten one of the pringer x, the 40M ones, and I am always online, in other steam games I have no achievement problems

Hmm, that's weird, I know for sure that beating the first one should grant the achievement because it's what happened to me. I've also seen it happen with other people - though looking through youtube, the only one I've found so far that shows this is in spanish, but you can still check it if you want (I'm not sure if timestamps work here, but it's around 1:08:35 ~ 1:09:00+).

My best guess is that steam didn't recognize you being online (I had it happen to me a couple of times, though with different games), or perhaps it's just a bug like you said. Either way, I'm not sure what could help your situation other than "try again and hope for the best" =/

I finally got it, it seems that it is mandatory to register the bosses in the dark record to get the achievement

Weird. My best guess is that Steam changed the requirements at some point, as it was kinda cheesy not having to complete the stage, but... it's still pretty weird nonetheless.

Regardless, congrats on 100%-ing the game