Some of that is a limitation of the RPG Maker system without plugins. The menu closing is due to the RPG Maker system and how it deals with common event calls.
I'll try to fix the battle system more later on. I definitely want to try to see if I can mess with things to make the potion generation smoother and more intuitive.
The insanity inflicting skill actually does more than just confuse. It actually adds some random effects to the battle. Originally, I was going to have insanity more contagious, but it is fairly broken already.
The poison wasn't supposed to work like that. Your party actually all resist poison to different degrees, but I haven't added in the system to make poison a gauge that fills. In the future, I'll remove their resistances and just have a gauge that needs to be filled.
I was considering battle backgrounds, but there were some issues with that because of one of the moves that I never had time to figure out (also a limitation of the base engine without plugins).
Voyd's basic attack is actually really strong, but it is designed to be used with a combo for maximum damage. Not sure which enemy you fought, but some enemies resist attacks from the wrong side. The game does mention this when the mechanic first applies, including in one of the skills' description.
Everyone has a different purpose with their skills and attacks (explained in the tutorial if not skipped):
Tulu: AoE basic, debuff, remove buff, add buff, aoe, boss killer, Ult: Anti all (the game gives a pretty direct hint on how to activate her Ult in the battle style tutorial). Can also learn debuff/boss killer, mob clearer, and finisher. (She is meant to kill bosses and set up the enemies for the party or kill enemies)
Nol: HP Depletion basic (random target- not entirely spammable), Item generation, AoE, Anti-Tank, Debuffer, Enemy/Boss Killer, buffer, protector, utility, healer, survivalist, Ult: Anti enemy / Anti final boss (The game gives a hint on how to activate this in the battle style tutorial). (She is meant to be all purpose)
Voyd: Anti target basic, item generation, AoE, debuffer, Ult: Anti enemy/boss (This should activate automatically with use of Voyd unless the player spams basic attacks). (He is meant as an ulter)
Nara: Mode based basic (Damage, Side based AoE, Healing, Buff, Void Side removal), Debuff, Survival, Mode change, Ult: Anti enemy (The game gives a small hint on how to activate this in the battle style tutorial, but it is meant to be discovered only by players trying to fiddle around with her). (She is sort of all purpose, but harder to use than Nol. Set up right, she is both anti-army and potentially anti-boss.)
There is an item you are supposed to use when you enter the caves. You should start with four of them, can make more, and two of the signs hint at it (one outside the cave, one in the cave) - they tell you to bring a light and there is an item/skill called Light Potion. One of the signs tells you to check your inventory. There is a secret that you can't obtain unless you use this item/skill in the cave. I'll be trying to fix that later on to be more clear.
Not sure which potions are broken. I checked and none of them or the items seem to be broken? No item in the game has scope self, for one. Only a few skills have scope none (actually, some skills have scope self, but the descriptions shouldn't suggest being able to use it on someone else) and they all seem to be working as intended. I do have some scope all/random though. Unless you had a double input for some reason, though that I can't really help if that happened. Unless you were using a Stockpile skill, but the name of the skillset is Stockpile and the game mentions that you stored the item (and the battle tutorial mentions it if not skipped). I do intend to change stockpile and use gift completely later though.
The encounter rate is high on purpose because it is supposed to push you to use a skill/item, which triggers a hidden event that lets you somewhat choose when to have encounters. I think you start with some of that item to hint at the player using them.
I'll see about adding some music to the caves later if I can find some appropriate music. I wanted it to be a bit quieter in the cave, but I can see that adding music might be useful. I'll try to make the battle start sound a bit lower than it is now.
Ummm... Actually, which version of the game did you play? Unless you are playing the archived/backup version, which is not marked as windows version (and is marked as v0.0.0.0.a when the other files are marked as v0.0.0.1.c.r9), almost no skill should do 0 damage unless you are attacking from the wrong side or it is meant to do 0 damage because all skills have a minimum damage that they deal as long as the enemy isn't immune. The game explains the side mechanic when you first encounter enemies that this mechanic applies to assuming you haven't already figured it out by then. The tutorial text should be repeatable with a key item.
Well, either way, with all the problems that RPG Maker MZ has without plugins, I'll probably remake this in Unity or Godot since they are more reliable and easier to program for, especially for what I want to do.