After you meet Frog in his forest home, you look for a way to help him.
Go to the Mountains
Go east from Dorino (near the south end of Zenan Bridge) to find the Denadoro Mountains go in.
Put Lucca in your party. Robo is a good second character for his strength. At the entrance of the Denadoro Mountains (east of Dorino) open the chest (300G), then battle the monsters.
Go north, and instead of using the ladder, go north along the river to the east of the ladder.
Open the chest (partially hidden by leaves to the left) (MirageHand), then go back one screen and go west toward the ladder. There will be a cutscene. To defeat the Ogan (the second monster you fight), first have Lucca use Flame Toss on it to burn its hammer, then just use normal attacks. Use this strategy on any other Ogans you encounter. After the battle, go north up the ladder.
Go southwest to reach an area with a chest (Revive).
Go north again, then go west behind the rock and open the chest there (Ether). Go north.
Open the chest north of where you fought the Ogan and Goblin (500G), then go east across the bridge. Slowly walk south if you want to avoid the Ogan that is lying in wait near the ladder. Then go north up the ladder and keep going north to reach the next area.
Walk slowly east if you want to avoid the Free Lancer that lands in front of you. You can avoid fighting it by walking south of it.
When the path splits, go north first to find a chest (Mid Ether). Go back south, then go east past the ladder to find another chest (Revive), then go north up the ladder and open the chest (Gold Helm). Go north up one more ladder and defeat the Ogan that attacks.
Go west and fight a Free Lancer and an Ogan, then go south and open the chest (Mid Tonic), then go north again, then west to the next area.
Run north through 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, after you go up the ladder, you can stay near the west wall if you want to avoid fighting, then open the chest to the northeast (600G), then heal up because you are about to fight several monsters in a row. Go north to the next area, and try to go west, and there will be several unavoidable battles.
After all the battles, go west to the next area and open the chest to the south (300G). Then go north to the water. Before you go south, go north and open the chest above the Free Lancers (Mid Tonic).
Next, go southwest to the edge of the water, but move toward the left as you fall down the waterfall. If you did it correctly, you will land near a chest. Open it (SilverStud), then walk southeast from the chest to fall down below. Go east to find another chest (SilverErng). Then follow the path and go north into the trees. From there, go north to the area where you fought a sequence of monsters, then go west.
You should be back in the area where you fell down the waterfall. Go northwest to the grassy area, and stay near the north wall if you want to avoid the Free Lancer. Open the chest to the left of the ladder (Mid Ether), then go down the ladder and stay near the west wall if you want to avoid a battle on the way to the exit.
In the next area, you can stay near the south wall as you go west to avoid a fight, then keep talking to the Kilwala until he gives you a Magic Tab. Then go southwest to the next area.
Before you use the save point, you might want to put Marle in your party and fight battles between here and the waterfall area until Marle and Crono learn the Dual Tech Ice Sword. Then come back here and save and use a Shelter at the sparkle if you wish, then follow the path. Open the chest on the way (Mid Ether), then after you go down the second ladder, go west onto the small ledge to find a Speed Tab.
Then put Lucca back into your party and continue on to reach the west side of the area where the Free Lancer is throwing stones. Run south past his stones and fall down the ladder. Open the chest (Shelter), then go east. You can avoid the Goblins by walking through the middle of the area. From there, follow the path, but don't get too close to the Free Lancer or you will have to fight.
When you reach the cave to the north, switch your party to Robo and Marle, then enter the cave. Go north and approach the sword. During the cutscene, say you're here for the Masamune.
Masa and Mune
In this battle, just use physical attacks on the one with the purple scarf. If you hit the other one, they will counterattack. If anyone gets inflicted with Chaos, use a Heal on them 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.
After the battle, there will be a cutscene. Afterward, go north and walk up to the Masamune. There will be a cutscene.
Go south to Porre and enter Tata's house, and talk to Tata to get the Hero Medal.
Then go northwest to the Cursed Woods, go north and climb down the ladder behind the bush, and talk to Frog. Then open the sparkling chest.
Leave the forest and go north, cross Zenan Bridge, then go northeast to Truce Canyon. Go through the canyon and use the Gate at the end to reach the End of Time. Use the northeast pillar of light to go to 1000 A.D., Medina Village. Go outside and go west to Melchior's hut, and talk to him. Then go back into the house in the village where you arrived, and check on the cupboard to use the Gate to return to the End of Time, and use the southwest pillar of light.