EDIT: I check a few videos on youtube of the final fight and no one could use items. I guess I was wrong.
Gjoerulv, I believe I have found a bug with materia growth. (Unless of course, you did this on purpose but I don't see why that would be the case.) I was leveling up near Wutai (however you spell it) and fighting against those giant turtle monsters whose name I cannot spell. My revive materia had 1 out of 3 stars. Once I got enough AP to reach the 2nd level (2 out of 3 stars) I actually gained two levels and went from 1 star to 3. The same thing happened with HP Plus materia. I was at 3 out of 5 stars, and once I got enough AP to reach 4 stars I went straight from 3 stars to 5 mastering the materia. This bug is bittersweet however as it can make the game too easy.
I have a question for you Gjoerulv. Why did you remove Flash from Slash-All materia if you didn't take out "remove" from exit materia? Doesn't it do nearly the same thing? I've never used flash and all I know is that it has a chance of instantly killing all enemies. "Remove", removes the enemies from the battle still giving you EXP and AP so its not much different from flash besides it costing 100 mp and being a spell. You can easily learn this before Temple of the Ancients, making the rest of all the random encounters in the game easy for the most part assuming you have enough money to buy ethers. Oh wait, I forgot, some materia skips a level when it levels up which causes it to master instantly, meaning that I can sell my glitchy mastered materia for loads of cash to buy hundreds of ethers so I can just "remove" everything in my sight in between boss fights....
Here are some suggestions to make the game harder (if these things are possible, I know nothing about hex editing or how the FFVII engine works):
1) Take out Remove from exit materia (you might as well leave it in Master Magic Materia since you've most likely defeated one of the toughest monsters in the game to get it)
2) Change Odin's "Steel Bladed Sword" from instant death, to heavy damage (or piercing magic damage, but NOT BOTH) to regular enemies, while leaving "Gunge Lance" for bosses the same as it is now. That way you can't deal heavy (or piercing) damage to bosses (or things immune to death) but Odin is still effective in regular fights without being too cheap as causing instant death. Why would take out Odin's instant death? For the same reason you took flash off of Slash-All materia and made Master Command flash. If you put a really difficult enemy in every area and you could just OHKO them with Odin (or Remove) that would defeat the purpose no?
For example, I know you intended to make those giant turtles near Wutai hard (I can tell because they have alot of HP and physical attacks do next to nothing on him) but I just OHKO them with Odin or Remove and get a reward of 800 AP. I think the 800 AP is a good reward for killing something that is abnormally "difficult" but Odin and Remove just make it easy AP. Talk about making the game easy, I've mastered things near Wutai before I've completed the Temple of the Ancients using your mod that I normally would not master until after Cloud rejoins your party in disc two. (Such as Restore, Revivie, and HP Plus materia.)
3)Leave master command and slash-all the way it is.
4)Fix the materia glitch I described before to prevent easy money.
Don't get me wrong though, these were just suggestions and so far I LOVE your mod. From what I've played my favorite parts were the First Reactor and Mt Nibel. I've seen the game over screen a few times in those places lol.