I'm going to keep track of my reports in this post.
EASY
-The Mud Imp ran away instead of dying at the end. You might change the enemy so the player won't get an easy win because it fled.
-The savestate I'm testing with is at the Magic Kingdom in the storyline. The End of Time screen won't let me substitute my players back in to form a full party. You could just automatically add Lucca and Marle back at the end, since by the time the Coliseum is available (End of Time), they'll already be in for good.
MEDIUM
-The Tubster on Level 6 is a pretty weak enemy just because he only has one attack (two actually, but the second is VERY rare). You could bump him down a few notches and let the Goon replace him.
-The Black Omen enemies are still awarding high-end items like HyperEthers. We could just have something in the events to automatically deduct one of the item an enemy gives, but we can't do that for charms.
HARD
-Should the Omnicrone Spekkio go before the Pink Nu?
-OUCH! We'll have to make sure the Super Armor really lets a single player beat this difficulty. If he can't, we might have to tone it down somewhat.
OVERALL
-Since the music track is a little short, we could use it for the first room, something else for the second, and Great Battle (used with Masamune in Denandoro Mts.) for the level 7 monster.
-Sometimes the battles just don't start at the very beginning, but I can't isolate why. It's only happened like 2 times out of 10.