New Enemies in Old Areas?

Something similar to this has occurred in Igavania titles since Symphony of the Night, albeit to a limited extent.

In SotN, after you progress to a certain point in Dracula's Castle, you'll no longer encounter the lone Warg at the very beginning of the Entrance (just outside it). There will instead be an Owl Knight guarding that area.

In Portrait of Ruin, backtracking to certain rooms after witnessing story-related cutscenes in them will lead to encountering more enemies (not necessarily new ones).

Maybe we'll see something like that in Bloodstained after all.

Owl knight replaces warg.
Zombie Soldiers replace the first Skeleton soldiers.
Slogra and Gaibon appear early before the Alchemy lab.
Armor Lord in the Outer Wall doesn't respawn until you leave the area.

In Portrait of Ruin the first Dragon Zombie never re-spawns.

Did I miss anything?

Wasn't a problem in Circle of the Moon. In CotM there were an absurd number of enemies, but none of the drops were affected, and none of the enemies disappeared entirely to my knowledge (unlike in Metroid Prime, where certain enemies couldn't be found again after certain points). Then again, CotM didn't subscribe to the philosophy that every enemy needed to drop something unique.

Even so, I don't think it's that big of a problem, as long as the enemies swapped out aren't unique. Are players really going to miss a handful of common enemies like axe armors and skeletons (well, the Bloodstained equivalent) in a room here and there? Granted, this is something that works better if the enemy placement is designed with that in mind.

I wouldn't mind it being something that only happens in Nightmare Mode, though. The point of it is to increase the difficulty, after all.

Also, it seems like there were some cases of enemy replacement I missed in SotN, however minor they were - and I forgot about Aria of Sorrow's tendency of placing enemies in old boss rooms. Which reminds me - one thing I don't miss about Circle of the Moon's enemy placement was that it sometimes placed powerful enemies, with unique and valuable drops, in very out of the way areas the player has already gone through, such as secret rooms and the first boss room, which wasn't exactly on the way to anything. But in general, I liked how it replaced some enemies, especially in "hub" areas, with tougher enemies to surprise the player. Given how some areas connected to each other, and how there were only five warp points, the player would often go back to old areas, so I think there was value in changing things up.

My suggestion would be evil pillars. I've seen them in ARPG games. Sometimes they are statues, stones or what not. They reward you with more enemies if you choose to activate them. This could be a thing if these pillars were spawned at random perhaps?

If not, well, having enemies respawn would be cool in the nightmare difficulty, along with more aggressive behaviours. I actually want more levels than just normal and nightmare, just to find that sweet spot. I blaim all the ARPGs I've been playing. I am fine with normal really, and I hope Nightmare Difficulty can add more flavor to the longterm player.

Galamoth I have heard about JoJo on and off, and sadly I know nothing about that project. Pinpoint me to the right direction with a PM and I would gladly check it out.

Also worth mentioning, as what we have touched upon before, is this: bloodstainedfanforums.com/thread/2463/choosing-difficulty-poll

"Meet a Monster: The SotN Advanced Style
You make a test in the beginning, that test will decide what difficulty you will end up with. New players might get easy and so on. The way this mode would be handled could be anyones guess. It might give you items at the start, or in hard difficulty perhaps make your luck less, or enemies punch harder and have more health."

In other words; Will the game understand you being an IGAvaniac, or a casual player which is new to the genre. This by letting the casual players get an potion to start out with, or a gear, to make the game a bit easier right from the start. It could be a trail early on, or how much damage you get from perhaps the first boss Vepar. Who knows. It would apply on the normal difficulty with one or two items added to your inventory only.

It really would change the 'normal' to 'easier than normal', and it worked fine in Castlevania Symphony of the Night.

When it comes to enemies. I guess they could be easier to kill, or less.. If you would to get a super bad start..?