I finished MM6 with a party of 2 wizards and 2 druids.
Some people mock MM6 as being "Magic and Magic" because physical damage options are so weak. MM6 has only 3 mastery tiers, which means that a lot of weapons are missing +1 damage per skillpoint options like in MM7. Additionally, MM6 has no Armsmaster skill like in MM7. As a result: if you thought knights were a waste of space in MM7, they are even worse in MM6.
Another common misconception is that the best party in MM6 is 2 wizards and 2 clerics. This works well in MM7 if you take the dark path... but in MM6:
-Light and Dark are incredibly weak for damage. In MM6: there is no Light Bolt, which means that light element only has prismatic light (garbage/waste of SP) and Sunray (if you want to do that much damage instantly you might as well throw a Dragon Breath instead... and Sunray does magic damage which half of the enemies in the game are immune to). If I remember properly, MM6 has no elemental summon either. The only reason to throw any points into light magic are Golden Touch (converts items to gold, making merchant skill obsolete) and a bunch of protections and buffs. Paralyze isn't even worth it - costs 50 SP and uses magic resistance, so you're better off just nuking foes with elemental damage instead.
-Dark element has a lot of useful offensive abilities but they cost way too much to be useful.
-Toxic Cloud costs 20 SP and does +1-10 damage per skillpoint in poison damage. You might as well use Implosion, which has a better element (physical damage!!!) and costs the same.
-Shrapmetal costs 50 SP and does a bit under twice the damage of Fire Blast on average... for over triple the cost. The only redeeming factor about MM6 Shrapmetal is that it does physical damage.
-Dragon Breath and Armageddon cost somewhere around 100 SP. Since there's no grandmaster meditation skill, this means that you will be running out of SP very quickly. Not useful in practice.
-Moon Ray is (ironically) the best healing ability in the game. Otherwise... its damage sucks and it can only be used outdoors at night.
-Clerics have almost no combat viability in MM6. Light/Dark are just plain bad in practice, and their other damaging abilities are also a waste of SP. Oh, and they do magic damage, which almost everything's immune to. Most clerics' debuff abilities also use magic resistance.
The choice is clear - druids absolutely rule MM6. They can heal just as well as any cleric (short of divine intervention, but you could just use Lloyd's Beacon Intervention instead, and if you want divine intervention so badly, that's what your wizard's for). They also get elemental magic (drop meteors on enemies, point-blank poison spray/fireblast/sparks, throw fireballs, and every way to be obnoxious in combat that you can think of). Like I mentioned above, I recommend 2 wizards and 2 druids. Other good variations would be: 1 wizard and 3 druids (3 healers, and everyone in your party can do a lot of elemental damage), or perhaps 2 druids, a wizard, and a paladin (if you want a character to absorb damage).
Druids only have 2 disadvantages in MM6: they are weak in the starting game (all casters in every Might and Magic game are weak in the early game) and they aren't able to use light/dark (which isn't a problem because you really only need one character with light/dark "prismatic" magic. As a general rule: Want to win MM6? Make your party 2 druids, a wizard, and something else (preferably another wizard or druid)
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The other big balance problem in MM6: there is no "protection from conditions", which means that you will find your characters being instantly KO'd, instantly dying, or even being instantly eradicated - no matter how much health they have. Supposedly some instant conditions and effects have their chance decreased with various elemental resistances. but in MM6, there is no guaranteed protection against any condition.
If you are having problems with being eradicated in the Control Center, there is an AI glitch with corners, walls, and ranged AI. If you see one of the robots that can instantly eradicate, you can edge around a corner and get them stuck on a wall. 2 of your characters will be able to see it (and use ranged attacks against it). On the other hand, the robot's ranged attack will consistently discharge into the wall, rendering it completely ineffective. Now enter turn-based mode, have the characters out of the line-of-sight block while the other characters hammer the robot into the scrapyard.
As a general rule, this glitch works on most ranged enemies indoors.
The best way to fight enemies that cause instant KO/death/eradication is to avoid taking any damage from them in the first place. Flight and keeping your distance are the best protection.
Other times, the best defense is a good offense. Get a 2 druid/2 wizard party with "of Fire Magic" and "of Water Magic" items. Raise their fire and water skills to something ridiculous like level 30. Now you can spend the rest of the game charging at enemies and instantly vaporizing them at close range with poison spray and fireblast.