Alright, so items!
Items in RPGs generally aren't toooo bad so there's not a lot to be done with them really. Potions and such are useful, status effects are always nice to get rid of, reviving is essential, all that business. You could make a case for one battle stat boosters being bad but that honestly, I feel, comes down to personal preference. With that said, the vast majority of items either get used a lot and get mundane, or they rarely get used and as a result feel useless. The one seemingly universal exception to this is SP/MP restoratives, which always seem useful and it's always a decision to use them or not.
So! What's the solution? I kind've took a bit from pokemon in this, items in there tend to be fairly universally useful, you never think "oh, gotta use more potions to keep going", it's usually something you use in battle to keep a pokemon alive, for tactical reasons, and even then it's not a no brainer. So, what does pokemon do different? For one, really strong elemetal weaknesses/strengths. We've got that, sort've, with curtains. This results in attacks either being piddling, but capable of whittling you down, or one shotting you. There's not a lot of inbetween. Two, full heals are common and easily available. It's easy enough to go back to a pokecenter most of the time to heal. Three, enemy encounters are very easy to predict. They happen in grass, caves, and in trainer battles. The world isn't constantly out to get you. Four, healing pokemon with other abilities is exceedingly rare, and usually has strings attached. This empowers items because you can't just grab a "healing pokemon" and invalidate items. This results in...
One: You use potions either when you're tired of a dungeon/game segment, or want to move forward in a hurry, and don't want to walk back to heal and come back to the dungeon. This is acceptable, if not ideal. You really shouldn't be trying to prevent the player from expediting something they find painful, similarly if they're looking forward to more of the game, great!
Two: You use them in a fight when you feel in danger of losing, not just on random mooks, usually on bosses/particularly tough random enemies. This is ideal. Items are a tactical decision, you don't just use them because you're low on HP, they're a limited resource, you never know when you're going to get more, barring a run back to town to buy more.
So, how will this effect the game? Items will be powerful and limited, to an extent. Shops will contain them, rare items will be in the dungeon only. I don't intend to run a full team of characters in game, I'm even considering just having one character, maybe two through the game, so, avoiding as much damage as possible is ideal, but items still allow you to sort've "cheat" a mistake. More powerful items will allow you to cheat entire fights, make boss fights notably easier, but again usually have strings attached to obtaining them, extra fights, whatever. Some examples -
Self auto life item: These will be far more common if I run a single character "model", as every fight is a life or death situation when you've only got one character. Otherwise rare-ish, maybe the top end item in the player shop. Revives the character it's used on at half max health when they die, no lost turn, nothin. Allows you to keep up momentum in battles you're having difficulty with, if even not solving the problem explicitly.
Crystals: These are the big ones. Rarest of the rare. One per strata. (The dungeon design consists of four "segments", four bosses, four tilesets, etc, maybe a fifth one for post game content.) Intended as boss cheating items, easymode, that sorta thing. Will provide huge defense bonuses to all elements, including physical and status effects, (You'll still be vulnerable to whatever curtain is going on, so you're not 100% safe, but if the boss does something funky like summon off element ADDs then it'll basically make you immune to them, for instance), banishes the current curtain (if the boss activates more curtains later on then it won't stop them), basically turns the fight into a slugging match, which, with the player character's skills and item stores will obviously make the fight notably easier. Not necessarily a "skip fight" button, but pretty damn close. Intended for bosses or rare monsters/minibosses, obviously, but if you want to waste them on mooks, be my guest.
The gambit of HP restoratives: The game plan for this category is to make them semi common, not nessacerily valuable, but notable treasures, that do exactly what you think they do. Not insignificantly cheap but cheap enough that you could spam them if you really needed to.
The identical gambit of MP restoratives: Rarer then HP restoratives, expensive in shop, uncommonly found in dungeons. MP will be a big deal for the curtain system, but there will also be elemental weapons, soooo MP is reserved for high power attacks. Elemental magic may also have nerf effects tied to it (fire damage lowers attack, elec lowers speed, etc), but I'm not 100% sure of that. The point is: Magic will be powerful, enough so to blow through an enemy if you're willing to all in with it, so MP restoratives are going to be something of a bottleneck to that.
Curtain items: Undecided. If they exist they'll just activate a curtain for you. Crystals will NOT banish allid curtains if allied curtains go in in any way shape or form.
Obviously this isn't a final list and these are working names. Still, a bit of content for you!
Up to floor 10, also. When all the floors are done I'll put a cursory effort towards uploading images of all the floors on the internet for people to look at and comment on. I'm not terribly proud of most of them, but I'm also not terribly ashamed of them.