After defeating the Reptites, you manage to travel to a different era.
Leave the Cave
Exit the cave and head right. Go into the skyway and walk up to be transported. Exit.
Head over to that complex to the right, Enhasa.
Head to the upper-right area and check on the book on the table.
Then go up the upper left stairs to meet a strange kid. After that, continue up the stairs and check the book on the table.
Before moving on, step on that blue circle below you to heal up everything.
Finally go to the bottom middle of the big room, by where you entered, and open the book there. Go through the door that appears.
Check on the Nu to fight six Nus.
These guys have two attacks: take your HP down to 1, OR damage you by 1. This means that if your HP is 1 and they hit you with that "damage by 1" attack, you die. So, whenever your HP is 1, heal up. I like to use Falcon Hit to get three of the Nus at once. It should only take two Falcon Hits to kill a row.
Before leaving Enhasa, use that blue circle again to heal up. Now exit, use the Land Bridge north of Enhasa, and continue on until you reach another complex, Kajar.
First, go to the upper left and open the book there. Then open the book at the bottom right. Finally open the book near the sleeping Nu. Head in the room that opens, and check the Poyozo Doll to get a Black Rock.
Now head through the door at the top right. In here, check the bottom right wall for a Tab.
Now just leave Kajar.
There's a cave opening to the right. What you want to do is go into caves, step into the light, and keep going up until you reach Zeal palace.
First, head left, up, and up the stairs, then down. Talk to a lady who has a little sapling. Tell her NOT to burn it, but to plant it. Otherwise you'll miss out on something later.
Now, talk to the Nu who's walking around, and agree to scratch its back. Now, you can go back to Kajar, go through the upper right door, talk to the Nu looking at the bookshelf, and you'll scratch its back, and get a Tab.
Back in Zeal Palace, go into the door at the top right, then through the door on the right. Follow Schala out, then go through the top middle door in the main hall. Go up and watch Schala.
If you can beat Lavos now, go back to the End of Time via 65,000,000 BC and use the bucket (or telepod in a New Game +) for ending "A Slide Show?"
Now you can go into the room at the top left of the main hall by talking to the Nu. Go straight up through the door.
NOTE: Once you check on the red sparkle, you won't be able to leave the palace.
Check on the red sparkle.
Before moving on, replace Ayla with Lucca, and make everyone in your active party wear Ruby Vests.
Now go back to the door that Schala opened with her pendant, and walk up to it to open it. Go in.
After the scene, you have to fight.
You can lose this battle if you don't feel like fighting, though you'll miss out on good experience.
Keep HP above 120.
Don't let Golem alone too long, he has a sort of fireball attack that affects a single character and will surely kill them. I recommend starting right away with Lightning2, then as soon as you can, Fire.
If you cast an elemental on Golem, he'll counter with that element, though he's slow about it. Since you have Ruby Vests, it's best to let Lucca attack with fire. Since Golem is slow to counter, you can use Lightning2 on him and then follow right away with Fire, and Golem won't hit with lightning. If you hit Golem with a physical attack, he counters with Iron Orb, which halves your HP.
Whether you win or lose, the same thing happens.