Fridge Brilliance: Why can't you advance from Wizard to Mage if your alignment is too low? Because wizardry is demonic magic, and Evil Is Not a Toy. If you hit rock bottom on the Alignment scale before you're ready to become a Mage, you can't advance and negotiate a better Deal with the Devil, because the demons control you, not the other way around.
Game Breaker: Princess+Lich. The Princess gets two White hit-all attacks, the Lich gets four hit-all spells that can be anything except White. Add a cleric class for a medic and a High Sky monster to carry the unit, and watch it tear anything and everything that opposes it to shreds. Just remember to watch your Karma Meter.
Alternatively, you can ditch the cleric for another lich/sorcerer/muse/doll master and put some undead in front of the unit to tank instead of the high flying monster. Undead are completely invulnerable to anything that isn't white magic or healing (although that kills them incredibly quickly), so the unit has a lot of survivability even without a healer. You do lose some maneuverability, though, but your increased damage output would be worth it if there was anything that could survive the Princess+Lich combination in the first place.
Alternatively, since most bosses towards the later half of the game are low alignment and thus more vulnerable to white magic, Princess + 2 Seraphim with your choice of unit to do the tanking (Platinium Dragon anyone?) means a veritable hailstorm of white magic hit-all attacks.
Also Rashidi from the same game. If the player's Chaos Frame is low enough, they receive a special ending which implies the entire game was just one massive ploy on his part so he could be resurrected.
Tear Jerker: Depending on how the story plays out, Yushis vs Mizal, as well as Rauny vs Hikash.