So, idea: A Final Fantasy game set in the mechanics of Mega Man
Expanding on the idea:
Each "robot master" is represented by warriors of different classes, and instead of Copy Weapon you gain a crystal shard that allows you to turn into that warrior, however not boasting all the abilities they had.
Instead of having specific weaknesses, there will be Defense and Spirit status, the former means they endure physical attacks better and the later endures magic attacks better.
Now, onto the classes themselves:
(High Defense) Monk > Knight > Thief > Ranger (Low Defense)
(High Spirit) White Mage > Black Mage > Red Mage > Time Mage (Low Spirit)
(Neutral+) Dragoon > Warrior (Neutral)
Assuming the 28 points of health, this should mean: Mage classes will take 8, 7, 6 or 5 points of damage from Monk, Knight, Dragoon and Thief, but would receive 1, 2, 3 or 4 from other Mages. Similarly, Physical classes (Monk, Knight, Thief, Ranger) would receive between 1 and 4 from physical classes and 8 to 5 from Mage classes. Neutral+ and Neutral are exceptions, as they will always deal 4 or 2 respectively.
How should I put this in example? A Monk or Ranger will always deal 5 points of damage to White Mage at worst, but they can deal 8 points of damage to Time Mage.
As a note, Mages have limited energy to cast their skills (28 MP), but they recover 1 point per second (2 points required for their basic "B" attack).
As for how each class works (assuming this would be a romhack for a NES):
- Warrior: The class you start with. There's nothing special about it, has a short ranged slash attack. At least nothing is resistant to it...
- Dragoon: You would find this later on (maybe after defeating 4 other warriors), has a slightly longer attack than Warrior, but also boasts double jump and the ability to do a "!Jump" attack (by holding Down and pressing B) midair (normally in the descent of a jump) that damages anything on the way down while gaining a two seconds invulnerability from successfully landing a "!Jump" attack.
- Monk: Has a pitifully short ranged attack but that can hit rapidly (compare to Castlevania Aria of Sorrow's "Kaiser Knuckle"). Can regain 1HP per second by standing still for longer than 5 seconds.
- Knight: Possess the ability to ignore knockback, but not the brief "stun" normally caused from taking damage. It's main ability ("!Defend") is to reduce all damage to 1 (2 for a Magic Attack) by holding B, however this renders him immobile. Has the same range as Warrior.
- Thief: Fastest of all physical classes, the thief also benefits from the ability of charging for an attack that has the ability to steal items from enemies (basically, makes them drop a Potion or Hi-Potion, even Elixir or Phoenix Down if you were lucky. Those are Small Health, Big Health, E-Tank and 1-up). However has a short range (yet longer than Monk).
- Ranger: Most Megaman-sque class. It is able to shoot fast arrows and execute !RapidFire by charging the attack, which then releases a barrage of 4 arrows that negates mercy invulnerability.
- Whiite Mage: Main attack is Aero, which shoots out a small and slow ball of wind, but only one can be on screen at any time. Charging attack however uses Cure to heal 7 points of health for 7 points of magic. Holding Up before releasing a charged attack however results in Holy, which causes 8 damage (ignores resistance) to an enemy within the White Mage's line of sight at the cost of 28 MP.
- Black Mage: Main Attack alternates between Fire, Blizzard, Thunder (which are represented by a fireball, an ice spike and a lightning ball), which allows it to have up to three projectiles on screen. The Charged attack is Bio, which shoots out a cloud of poison that inflicts some damage and causes those hit by it to take 1 point of damage every 5 seconds for only 7 MP. Holding Up before releasing a charged attack however results in Flare, which causes 8 damage (ignores resistance) to an enemy within the Black Mage's line of sight at the cost of 28 MP.
- Red Mage: Normally shoots up Aero "balls", but can also shoot Fire, Blizzard, Thunder, mimicking White and Black Mage. Main exception being that it can only have one projectile attack on screen. The charged attack is "!DualCast" with Cure and Bio simultaneously, however requiring 14 MP! Doesn't have a special Up release.
- Time Mage: Shoots out a single Comet from above itself in a downwards 15º angle, making it a bit difficulty to aim but at least having up to four of these on screen. The charged attack is Meteor, which is like Astro Crush but requires 14 MP and has a chance to miss (remember Power Stone? It can screw up that bad too...). Releasing the charge while holding Up results in Banish, which will destroy every enemy on screen for 28 MP, but won't work on bosses at all.