After learning about Tata and the Hero Medal, you look for Frog.
Put Lucca in your party (Robo's a good second character for his strength) and go to the Denadoro Mountains, east of Dorino. Open the chest (300G), then fight (or avoid the monsters by going to the right when the Bellbirds are out of the way).
Climb the Denadoro Mountains
Go up, and instead of taking the ladder, exit to the right of it where the river exits the screen.
Open the chest (partially hidden by leaves to the left) (MirageHand), then go back one screen and head for the ladder. To beat the Ogan (second monster you fight), first have Lucca use Flame Toss on it to burn its hammer, then just use normal attacks. Climb the ladder.
Exit via the bottom left, and there's another chest (Revive).
Go back one screen, and walk left behind the rock for the chest there (Ether). Go north.
Open the chest above where you fought the goblins (500G), then head right over the bridge. Walk slowly at this next part, there's an Ogan lying in wait. Let it run in front of you, then when it's back under the tree, head up the ladder. Keep going until you get to the next area.
Walk slowly again, a Free Lancer will fall in front of you. Avoid it by walking under it.
When the path splits, go up first for a chest (Mid Ether). Go back down, then head right, past the ladder for a chest (Revive), then up the ladder and open the chest (Gold Helm). Go up one more ladder.
After heading left and a fight with a Free Lancer and an Ogan, go down for a chest (Mid Tonic), then back up and left to the next area.
Run up the next area to avoid getting hit by the Free Lancer's stones, and open the chest on the way (Mid Ether).
In the next area, just hug the left edge and go around for a chest (600G), then heal up (you're about to fight a few monsters in a row) and move on.
After all the fights, go to the next area and open the chest below (300G). Then head up. To avoid fighting the Free Lancers, hug the top of the path, then go to the left and above them for the chest (Mid Tonic).
Next, walk to the bottom left of the screen. You'll want to fall down the waterfall (trust me). Hold down the left button as you fall. Get the chest (SilverStud), then walk up to the ledge just below the chest to fall down. Head right for another chest (SilverErng). Then follow the path into the trees.
Make your way back to the screen where you fell down the waterfall. Head left, hug the top of the path and open the chest to the left (Mid Ether), then go down the ladder and hug the left as you exit.
In the next screen, hug the bottom, then keep bugging the white fluffy guy until he gives you a Magic Tab. Then head to the next screen.
Save, then follow the path. Open the chest on the way (Mid Ether), then after you go down the second ladder, head left onto the small ledge for a Speed Tab.
Before heading to the next area, make sure Marle and Crono know the Ice Sword tech. Your best bet is to go back to the waterfall and fight the Free Lancers and Bellbird until you learn the tech.
Then put Lucca back into your party and move on to the area where the Free Lancer is throwing stones again. Run past his stones and fall down the ladder. Open the chest (Shelter), then head through the middle of the Goblins to avoid them. Follow the path.
When you get to the cave, switch your party to Robo and Marle.
Say you're here for the Masamune.
Masa and Mune
In this fight, just use physical attacks on the guy with the purple scarf. If you hit the other guy, they'll counterattack. Anyone gets chaosed, heal right away.
Use Ice Sword and have Robo heal. If Masamune is storing tornado energy, have Crono use Slash on him right away. Keep HP above 100.
Go up and get the Masamune.
Go to Tata's house, in Porre, and talk to Tata to get the Hero Medal.
Getting the Hero Medal from Tata opens up a new ending. Beat Lavos now if you can, for ending "The Unknown Past"
Then go to the Cursed Woods and talk to Frog. Open the sparkling chest.
Leaving the Cursed Woods this time was the first time I encountered a Nu here, so see the end of "The Hero Appears" for strategy and how to fight it.
Now go to the Gate in Truce Canyon to get to the End of Time. Use the pillar to 1000 A.D., Medina Village. Go to Melchior's hut and talk to him.