In this Magic Cake-induced dream of Ness's, he dreams that he is Poo, the prince of a land in the far East called Dalaam. Poo's mentor tells him that it is time for him to undertake the final trial of his Mu training.
Make your Way to the Mu Training Ground
Take the items from the gift boxes, and then leave the palace, talking to people on the way. Go toward the southeast part of town. You should talk to people and visit the houses. There are some treasure chests around, and people aren't all that bothered when you take their stuff. They all seem to love you, so it's cool. I think.
Anyway, once you reach the southeast part of town, you'll meet the Star Master at the base of the rope that leads to the peak where you will complete your Mu training. The Star Master will say that he'll meet up with you later, once you're ready for the powerful training that he has to offer.
Complete your Mu Training
After he disappears, climb up the rope. Once you reach the top, you will automatically sit down for your final Mu training trial. A girl from the palace will attempt to call you away from your training, but this is a trap! It's actually part of the test, and to pass, you have to ignore the girl and not press any buttons on the controller. If you mess up, go back to the palace to talk to the master, then go back and try again.
Once that part is done, you will experience the final trial. To pass, say Yes to every option (gruesome though it might be). After the trial is over, you emerge from the state of Mu, and a man from the palace tells you that you succeeded, and that you should return to the palace to tell the master. And no, this time it isn't a trap.
When you speak to your master, he will tell you of your destiny to join Ness and the others in the fight against Giygas. He tells you to go meet them in Summers. You gain a large number of levels, and then you teleport to Summers.
Visit the Secret Upper Room of the Museum
Once Poo introduces himself, he becomes a member of your party, to form the legendary group of three boys and a girl who will bring Gigyas down! Sweet! But you're a long way away from Giygas, still. What's next? Well, if you tried visiting the museum in town, you'll know that there's a secret upper room that a guard wouldn't allow you to enter. But it turns out that Poo carries a tiny ruby with him that the guard will accept as a bribe.
Go up to the museum room and give the guard the ruby. Then go on into the room. A couple of monsters will attack you. It's pretty easy to avoid the one on the far right, but the one on the left will probably touch you. Freeze attacks are pretty good against them.
Read the Ancient Hieroglyphs
Now, you should check out the plaque next to the giant piece of rock on display. It turns out that Poo knows how to read the hieroglyphs, so he reads it. The words are cryptic, but they were written by the ancient people of Scaraba who built the pyramids to protect against alien invaders. Apparently, these aliens will be reborn every millenium to attack Earth.
The slab goes on to mention a "place out of time," which can be reached by going to the Deep Darkness with the Hawk Eye, and from there going to the Lost Underworld.
Finally, the slab mentions the sphinx, which waits for a hero. It says to "dance in front of the sphinx" and shows a diagram:
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The guard gives you a photo of the hieroglyphs as you leave.
Leave the Museum
The alien invaders sound like Giygas and its henchmen. As for the rest, Poo tells you that you should go to Scaraba and visit the pyramid. As you leave the museum, however, the phone rings. It's Mr. Spoon from the Fourside Dinosaur Museum. He tells you of an amazing discovery before hanging up.
Go to the Fourside Museum
You can go straight to Scaraba if you really want to, but you should probably go to Fourside first. There are some opportunities at this point to gain a lot of levels before going to Scaraba, which will help out a lot, because Scaraba is tough.