After you meet Will's cousin Neil and explore the Condor in the Nazca Plain, you find yourself in the Sky Garden.
Find the Orbs
In the Sky Garden, you find several people of the Moon Tribe. One of them says that you need to find the hidden orbs here, and you should find them in clockwise order. Another says that you can jump off of the tiles to see the upside-down world.
There is a door to the Dark Space in the northwest corner of this first room. After saving, go back to the northeast, where you entered the room, and use the northeast exit that is just south of the first Moon Tribe Shadow that you saw.
Northeast Sky Garden
There are four Sphinx statues near the entrance. Go south to find two Nitropedes. Kill them, but be careful of the bombs that they drop when they die. Go south, then east, and kill more Nitropedes. Go north to find two Blue Cybers. They shoot lasers, and they can also shoot their hands forward as projectiles. Go north to find another pair of Blue Cybers. After getting rid of them, go north up the stairs and kill the Nitropede, then go east and kill the other Nitropede. Go south down the stairs to reach a large area. There are several Nitropedes here and some Blue Cybers. After killing them, go northeast and open the chest to get Red Jewel #18.
Now go south and go to the bottom of the large area. Jump off of the cliff in the south wall. You will flip to the dark side of the garden. There are Dinapedes here, which drop bombs more forcefully, and there are Red Cybers, which shoot lasers and their fists, but their fists come back like a boomerang. Go northeast from there to find two Dinapedes and several Red Cybers. Keep going east to reach the northeast corner of the area, then go south and carefully go past the flame snake. Keep going south and kill the Red Cyber while avoiding the flame snake. Continue west past another flame snake. You reach a Dinapede. Kill it and go south. You reach a crossroads with a Red Cyber. Kill it, then go east and kill the Dinapede. Go southeast and jump off of the cliff to go back to the other side. You find a chest that contains an herb, as well as a Blue Cyber. Kill the Blue Cyber then jump down the cliff again.
Now go west and kill the remaining Dinapedes, then go west around the path and jump off the cliff at the end. Go east and kill the Nitropede, then continue going east to find a statue. Its sword wakes up and becomes a Slasher. Hit the sword until it disappears. Open the chest behind the statue to get a Crystal Orb.
Jump down the cliff again and follow the path to the crossroads, then go north, then west. Go to the south of the large area and jump down the cliff. Go northwest and follow the path to return to the first area of the Sky Garden. After you heal up and save, go to the southeast area of the garden.
Southeast Sky Garden
Go south and kill the Nitropede, then go south and go around to the Blue Cyber and kill it. Then go south down the ladder. Go east along the ledge, then go up the ladder at the end. Go north and kill the Blue Cyber, then go east to kill the Blue Cyber next to it. Go south and you find a statue that holds a Slasher. Kill the Slasher and then hold L or R to move the statue out of the way of the ramp. Go west and up the ladder, then run down the ramp.
Go north from the other ramp, then kill the Slasher that the statue holds. After you kill the sword, hold L or R to move the statue. There is a secret door behind it. Go in. You find a door to the Dark Space where you can transform into Freedan. Do so, then go back outside. Go up the stairs behind the statue and kill the Nitropede. Then go east and north and kill the Nitropede there. Continue going north and kill the Blue Cyber and the Nitropede. Then fall off of the cliff in this area.
Go east and kill the Dinapedes, then use the Dark Friar technique to kill the Red Cyber in the middle. Jump off the cliff on the east side.
Kill the Nitropedes and Blue Cyber here to open the path to the south. Go south and jump off of the cliff. Go west and kill the Dinapedes, then go east and kill the Red Cybers. Go east and kill the Dinapede, then go north and kill the Red Cyber to open the barrier so you can reach the chest. Avoid the flame snakes that come out and open the chest to get a Crystal Orb. Go back to the central area of the Sky Garden where the Moon Tribe is.
Southwest Sky Garden
When you are ready, go from the first area of the Sky Garden to the southwest. Go south and kill the Nitropede, then go west and kill the two Nitropedes and the Blue Cyber. The path opens to the north. There is a dead end to the south, so go north and kill the Nitropedes. Jump down the cliff here.
Go west and open the chest to get Red Jewel #19. Then go east and hit the switch, then jump off of the ledge again.
The path west is now open. Go west and kill the Blue Cyber. Stairs appear that allow you to go up to the ledge. Kill the Blue Cybers up there, then go south. Kill the Nitropede to open a path to the east. Then go west and kill the three Blue Cybers. Go north, then go east from the door to the Dark Space and jump off of the cliff.
Go east and use the Dark Friar attack to hit the switch from a distance so you don't get trapped by the pillars. Then go back and jump down the cliff. Go into the Dark Space and transform into Will. Leave the Dark Space and go south, then when you reach the treasure chest, go east. Run down the small ramp and keep running in order to reach the two statues on the right. Use Psycho Dash to destroy those statues. Go east. Before using the big ramp, jump down the cliff. Go east, then go north between the two rows of statues, avoiding the flame snake. Kill the Red Cyber to open the paths, then go east and kill the Dinapedes, then continue east and kill the red Cybers. Go south from there and kill the Stinger sword that the statue is holding. Go west and kill the Red Cyber, then go east and hold L or R to pull the statue onto the tile that is west of the statue. Go north, then west, then south, then west, and drop down the cliff. Use Psycho Dash to destroy the statues again, then go up the stairs and run down the big ramp. Open the chest at the end to get the Crystal Orb.
Return to the big central area with the Moon Tribe Shadows.
Northwest Sky Garden
Use the northwest exit from the central Sky Garden area. Go south and kill the Blue Cyber, then go south and use the big ramp. You have to press up in order to reach the small ramp to the left. On the other side, kill the Blue Cybers and the Nitropede. Go north, then use the big ramp, but when you jump off of the little ramp, hold left in order to stop in the middle rather than going up the second ramp.
Kill the Nitropede, then go south and kill the other Nitropede. Go south and jump off of the cliff. Go east and kill all of the Dinapedes. Go east, then south to find a statue holding a Stinger sword. Use Freedan's Dark Friar move to hit the Stinger, then kill the Stinger when it floats to you. If you need to transform into Freedan, go north, then west, and you reach a Dark Space door. Back at the statue with the sword, kill the sword as described above, then hold L or R to move the statue onto the switch to its left. The statue below you will disappear. Before you go south, go west, continuing west instead of going down the cliff, then kill all of the enemies down below. Go back to the cliff that you passed, and jump down it. Kill all of the enemies to the east, then go east and south and kill the enemies there. Go back north and jump from the cliff, then go east, then go south past where the statue was. Kill the Red Cybers, then go to the southeast corner and jump from the cliff. Go north past the ramp and kill all of the enemies there.
Finally, go to the big ramp. If you press up after going down the ramp, you reach an herb. If you go down after using the ramp, you reach the Crystal Orb. Go back to the central area after you get the orb. To reach that area, go to the dark side of the garden and go north from the statue that is holding the sword. Keep going north, then jump down the ledge, then jump down the cliff. Use the big ramp to return to the entrance of this area.
Put the Orbs in Place
You should have four orbs now. Equip them and use them on the round holes in the middle of the first area of Sky Garden. After all four are in place, you can walk up the new bridge to the north to reach the boss area.
Go north up the stairs, which collapse as you go up. If you are Freedan, charge up the Dark Friar attack. At the platform at the top, go up close to Viper. The wind blows you back. As soon as Viper starts flapping its wings, hit it with Dark Friar. Step to the side to avoid the exploding feather attack. Don't worry about the large chunks of rock that float upward. These do not hit you. Sometimes Viper stops near the top of the platform. It will spit feathers/crystals at you. Stand to the left or right from Viper during this attack to avoid damage. At all other times, stand at the bottom of the platform to avoid the feather attacks. Soon Viper will be gone.
After the battle, go to the left side of the platform and jump down from the tile. You and the others will go to Mu.