Spoilers galore in today's protip, so if you don't want a 15 year old game spoiled, don't click on this link.

So, you made it to the last boss of Secret of Mana and he's walloping you pretty good. But I have a simple 3-step solution to get you through with a minimum of damage taken and time spent.

Step 1: Have the Boy equip the sword and have the other two cast Mana Magic on him
Step 2: Cast Lucid Barrier on the party
Step 3: Cast Moon Energy on the Boy
Step 4: Win!

Let's analyze these steps in-depth:

Step 1: Lets you actually hurt the end boss, fairly handy.
Step 2: Lucid Barrier makes it so that your party is immune to physical damage, so your party won't fall down, get stunned, or suffer any damage.
Step 3: Moon Energy makes every hit a critical hit, which means that the boss's HP is going to plummet.
Step 4: Game over, you win! And in record time.