Twincast, in an ideal world, I'd like to pretty much be comet except use the new "Level-based damage" routine or else maybe use caster's max HP (100% of it)? It should only work with Palom and Porom and should be disabled if the other twin isn't present. If possible, it should always use only Palom's stats no matter where he is in the setup.
Yes, that seems a bit tricky. I could never figure out the "Inferior Twin" issue myself. I think there's an old patch out there somewhere which disables Twin if Palom/Porom are not present. There are various Twincast hacks around, I made a couple myself that depending on the Superior Twin, a different spell is used, and the way it is designed easily allows for four spell possibilities with one of them revolving around a special conditional beyond chance.
Anyway, here's a preview of how I'm doing the character selection. Let me know what you guys think! 
(The patch is for 1.1 UN-headered)
http://www.timecave.net/ff4roguelikeifyer/FF4RL%20Base.ips
Don't actually run the roguelikeifyer on this version of the patch. It will mess everything up.
I just thought of a problem with the "clear the save file" idea. If you saved the same game in multiple files, you can get around it. Hm, I'll have to think more about it. Thanks anyways though ^_^
Nice bit of warning and explanation of the various functions. I also love FuSoYa as "God the Creator", it's fitting.
Palom/Porom - I like how their explanatory text is very similar to one another and good display of their abilities.
Yang - The mention of "boosting his physical defense" with Gird is interesting. Did you want anything more for Gird other than just a Protect Spell on self? Or did you already boost the power of Protect to make it worth using?
Edge - Everything accounted for.
Cid - Oh, nice detailed explanations about his planned new functions.
Edward - Haha; "He won't hide automatically". A crucial thing to tell players indeed, also great use of 'spoony' and nice description of the new Salve.
Tellah - Good description, makes the player immediately aware of Tellah's new role.
Kain - Fine explanation
Rosa - A nice change of role for Rosa and makes her distinct from Porom.
Rydia - Effect spells over direct damage... what does that imply in Black Magic? Pig, Toad, Venom, Stone, Stop, Drain, Psych, Weak, Fatal... alright that's a pretty good amount.
Paladin/Dark Knight - Another good use of juxtaposition. All around I really like this room.
And walking into the mirror of the back of the room sends me into the trees in the Village of Mist, heh. All in all it looks very promising, my only worry now comes with people picking characters, stripping them of their gear, and starting the character choice anew. Maybe start everyone with nothing, give the player 1000/2000 Gil and after the first choosing room, a second with a predesigned shop/s to get started?
The save file clearing isn't too difficult either. Instead of clearing 1024 bytes (I was wrong with the conversion before) you would clear 4096 Bytes to clear out all of the save data.