So, you want an easier game of M&M III, do you? Here's some things you can do to make the game a lot easier. If that's not what you want, DON'T read on... 'cause once you know, it's hard to resist the temptation of using them.
Are all the non-cheaters gone? Good. Now, on to the good stuff.
First off, I've got two passwords for the Magic Mirror that should make your game a lot easier. The first is DOE MEISTER. Say this at any Magic Mirror and you'll be instantly teleported to a secret room in the Dragon Cavern, normally only accessible by venturing into that dangerous place and Teleporting into the room. In this room, you'll find 2 million Gold! That should make the game a lot easier, shouldn't it? However, you can only get out again by using magic, or calling for Mr. Wizard's help. Mr. Wizard is likely to take away lots of experience if your characters are already at high levels, so if you're planning on doing this, do so when all your characters are still level 1. When this is the case, it won't cost you anything to ask Mr. Wizard for help.
The second Magic Mirror password I got for you is ORB MEISTER. This one will teleport you right in front of a King's Ultimate Power Orb hidden beneath the Pyramids. Bring the orb back to one of the three kings and you'll be 1 million experience richer!
There's another way to get experience quick and easy, though. Fill up all of your characters' backpacks and then find a monster lair (one that looks like a wagon or wooden shack) that you can destroy. Destroy it, and you'll get a "backpack full" message and the lair should reappear. You WILL receive the experience bonus, though. You can repeat the process as needed, getting the experience bonus you just received again. This works as long as your backpacks remain full.
Using the SNES version? Travis Roby informed me that you can use the L and R buttons to simply sidestep through deep forest and mountains without having the Pathfinder or Mountaineering Skill! Beware that your party members get hurt when you do this, however.
And then I have one last trick for everyone who just wants to get things over with. If you say BLASTOFF at any Magic Mirror, you can view the end-game sequence. You'll also need the initialization code though, which you're supposed to find in the game. Blackwind tells you one half and Greywind the other. You can also find out the code by visiting some statues in the Pyramid complex beneath area A2.
That's all of the M&M III cheats I know of at this time. Happy cheating!