So, worth knowing: Grotto bosses have rare drops with a 2% chance of dropping. Due to the way the RNG works, using the quick save and heal, it's possible to manipulate your chances to always get their 2% drop item, provided you don't use a Coup de Grace attack and they don't summon an ally.
Considering some of these items are worth getting four times, it's worth knowing.
This is the link to the applet that does the math for you.
It's pretty simple.
First, make sure you can use the heal spell on your party six or seven times without maxing anyone's health, by lowering your HP.
Next, quick save inside the same room as the Grotto boss.
Then, turn off your DS.
After that, check your heal caster's Magic Mending and input it into the first box. Click the button by the box.
The number that appears is the lower value in the range your healer can heal for with one heal spell.
After that, heal party members about five times total, recording each heal's value into each of the lower boxes.
After you reach about five or six, click the bottom box.
You should see a few red numbers with a Java and CGI link next to them. You want there to be just one red number. If there's more, go back, heal again, and enter the new numbers. If there's just one, click it.
After that, things are relatively easy. A table should appear with red, white, and blue squares. You'll be considered "on" the square that's equal to the number of times you've healed already. You have to "progress" to the square right before a red one. To do that, you have to keep healing, even if you have max HP. The good news? Healing at max HP doesn't cost MP. Count the number of squares to the first red one and use multiheal to move four squares forward and heal to move one.
Once you do that, fight the boss. Fight normally, but don't use your Coup de Grace. When you win, as long as it didn't summon an enemy, you should have the 2% item.
This process is a lot simpler than it sounds, I promise!