Aha! I found time to make a post on this. >.>
Just going to throw all the ideas that were said before and mine into a consolidated post, to keep it all organized. I'm organizing it into Hard, Medium and Easy restrictions to hopefully make it a little bit easier to decide which rules should be generated at the same time. My thoughts are that rules that have less of an impact should be more likely to be rules five or six, so that if somebody chooses to only use one rule it's still likely to end up at least a little challenging, but if somebody chooses to use six it's less likely to be impossible. I assume that at least a couple ideas will be dumped, but hopefully the majority should work out.
** Signifies that this challenge should only be available if "Gameshark Codes" is selected. Well, it would be more along the lines of hacks or cheat codes for FF6, but you get my drift.
// Signifies which challenges this challenge should not be paired with.
======Hard======
Low Level - Must be at lowest possible level.
Mandatory Battles Only - May not fight any battles that aren't strictly necessary to complete the game.
No Magic - Cannot use Magic at all.
Natural Magic - Cannot learn spells from Espers or equipment (Doesn't quite overlap with No Magic).
No Equipment - Characters must be de-equipped of all equipment ASAP if possible.
No Items - Cannot use Items at all.
No Specials - Cannot use characters' special moves in battle at all. Includes Rage.
Solo Character - Only use one chosen character for anything where it is possible to use them (the generator probably shouldn't choose Umaro or Gogo).
**Note: Solo character challenge can be enhanced if you allow "Gameshark Codes" by making the character available always.
CES - May not recruit anybody in the WoR (personally I'm not a fan of this challenge, but it's so ubiquitous that it obviously should be included). //Solo Character Challenge
Hardcore - If you game over once, you lose the challenge.
**Randomizer One - Must randomize the game using Dessyreqt's randomizer. (
link)
**Randomizer Two - Must randomize the game using Abyssonym's randomizer. (
link)
**ROTDS - Must be run in Return of the Dark Sorcerer. (
link)
======Medium======
Under 26 000 steps - Game must be completed in fewer than 26 000 steps. Personally I prefer "fewest steps" as a concrete constraint instead of a "Do your best" sort of deal. It brings it more in line with the other challenges. Note that I'm trying to set a good ballpark for restrictions that would make a difference for many challenges (varying a little to make it interesting) while making it unlikely that challenges would go uncompleted, with some care. I may be too lenient or too strict for many challenges here, I'm not sure. ~9000 is around the minimum number of steps that the game can be completed in without game breaking glitches. Semi-casual attempts at not taking many steps on RetroAchievements.com (with no other restrictions like we have here) seem to be in the ~25 000 range, which is why I'm setting this as the strictest value.
Under 30 000 steps - Game must be completed in fewer than 30 000 steps.
Under 34 000 steps - Game must be completed in fewer than 34 000 steps.
//Obviously only one of these restrictions should be used at a time!
Under 10 hours - Game must be completed in fewer than 10 hours. Same deal as with the steps, my numbers may be a bit off. It's also hard because I can't tell what challenges they'll be paired with.
Under 12 hours - Game must be completed in fewer than 12 hours.
Under 14 hours - Game must be completed in fewer than 14 hours.
//Obviously only one of these restrictions should be used at a time!
Level Under 20 - Cannot breach level 20 by the end of the game.
Level Under 24 - Cannot breach level 24 by the end of the game.
Level Under 28 - Cannot breach level 28 by the end of the game.
//Obviously only one of these restrictions should be used at a time! These also shouldn't be paired with Low Level or Mandatory Battles Only.
Quad Character Challenge - Choose a party of four to use at random and you must use only characters out of those four whenever possible. //Solo Character, CES
**Quad character challenge can be enhanced if you allow "Gameshark Codes" by making the characters available always.
No Relics - May not use Relics //No Equipment
No Espers - May not equip Espers for their boosts or their Magic //Natural Magic (they don't overlap completely, but the only difference is that with the Natural Magic rule you can still level up with Esper boosts against enemies that don't give AP, and that's probably against the spirit of the challenge anyways).
Low Esper% - May not collect Espers that aren't strictly necessary to complete the game.
No Items in Battle - May not use Items in battle.
No Offensive Items - May not use Items that do damage. Note that I consider Shadow's scrolls to be special moves, not Battle Items.
No Healing Items - May not use Items that heal HP.
//These and No Items should not go together.
Shop Equipment Only //No Equipment
**Brave New World - Must be run in Brave New World. (Insane Difficulty is down right now! I'll provide a link when possible!)
======Easy======
No Escape - Cannot run from battles //Low Level, probably Level Under XX
No Shopping - Cannot buy from shops (unlikely to make as large a difference as in other titles).
No Attack Command - Cannot use Fight (Fight is almost worthless in FF6).
No Non-mandatory Inns/Healing Springs - Cannot heal at Inns unless forced to (unlikely to make a difference, FF6 is an extremely easy game to be self-sufficient in and you'd have to be very careful to craft a challenge where this rule would matter beyond a little minor effort, which wouldn't happen from random generation).
Front Row Only - All characters must be in the front row for the entire game.
Stamina/HP Espers Only - Can only equip Espers that boost Stamina/HP (Ramuh, Siren, Terrato, Shoat, Bahamut, Golem, Starlet)
MP/Speed/Vigour Espers Only - Can only equip Espers that boost MP/Speed/Vigour (Ifrit, Bismark, Odin, Raiden, Crusader, Phantom, Fenrir)
Boostless Espers Only - Can only equip Espers that give no boosts (Shiva, Palidor, Alexandr, Ragnarok, Kirin, Carbunkl, Sraphim, Unicorn, Phoenix)
//None of these go together with each other, Natural Magic, or No Espers. Boostless Espers Only should not be paired with No Magic.
No Paladin Shield - Cannot uncurse the Cursed Shield (It's one piece of equipment, but it's a big one!) //No Equipment, Shop Equipment Only
Active Mode, Battle Speed 1 - Must set Battle speed to 1 and use Active ATB for the entire game.
Maybe I'll think of some more ideas, in which case I'll add to the list.