Get back into Potos Village:
If you want to get back inside the village you were banished from, you must have all 3 characters. Then walk up to the man blocking the entrance, and rapidly push the SELECT button while holding the UP button against the man. Eventually you would will push your way through him, and be back into Potos Village. Note that this trick might not work in escaping from Potos Village, so make sure you have the Flammie Drum before you attempt this.

Avoid magic attacks using pygmy hammer/Moogle belt:
Whenever an enemy character casts an attack spell on you or an ally use the pygmy hammer / moogle belt on the character being attacked , do this twice before the spell animation ends and if done correctly the character will completly avoid taking any damage. This trick is especially useful when you are fighting the Mana beast.

9th Sword Orb:
Here is how to get the "Mana Sword" permanently, and without a cheating device!

Fly to the ice country on Flammie and look for a small circular island off the immediate coast (trial and error are best here, but its NOT those little itty bitty ice chunks everywhere). You'll know its the right island if you are in a frozen grove with Neko surrounded by purple crystals (this looks like the same area you may encounter Neko on the way to the Ice Palace to fight Frost Gigas).

After that, Save the Game with Neko. Immediately after, do a soft reset (L + R + Select + Start). Start a New Game, and get to the Mantis Ant fighting as few (i.e. none) Rabites as possible. When you and Elliot take a dive into the pit, wait for him to say "You've got a sword don't you, use it!" WHILE THIS TEXT IS ON THE SCREEN, perform another soft reset. BE SURE TO HOLD THOSE FOUR BUTTONS FOR 5+ SECONDS. I don't know why those 5+ seconds are required, but they are. When you get back to the title screen, load the game you saved with Neko in the Ice Country. If you did the trick correctly, all three of your characters will be in the pit fighting the Mantis Ant! (If you did it wrong, you'll stare at a blank black screen and the game will freeze) Kill the weak boss (took me one hit...), and collect your "1st" sword orb again. Jema will pull you out and Timmy will call you to the elders house. Rather than risk a crash, call Flammie and high tail it to the nearest Watts location.

You now have the most broken weapon in Secret of Mana at your disposal, without needing to cast Mana Magic ever again.

*Final Note: This trick can be repeated if you wish, but do NOT forge your sword past level 9. The game will glitch and/or crash. You may get your Rusty Sword back, or you may corrupt your save file beyond repair.