After escaping the Great Pyramid and the Jackal, Neil takes you to the Tower of Babel in his plane.
Climb the Tower
Enter the door into the tower. Go all the way east until Will stops and says something. Check on the blue box between the two Freedan statues. You will find Red Jewel #50. This is the last red jewel in the game. You can't leave the tower yet, though, so go east.
There are some spikes to the east. Walk up the stairs toward the wall, then walk east along the wall. Go down the stairs at the end. Walk into the lasers blocking the door. Then check the sparkle on the floor. You'll get the Crystal Ring. Equip it, then go north through the laser beams.
Go west and watch the cutscene. Then keep going west. Talk to the floating souls as you go along if you want to learn more of the story. Go west and use the exit at the end.
Go east and talk to the souls. You will find a door. There is a Dark Space to the right of the door. Go inside to heal and save. Then go back out and go into the door to the left.
At the start of the battle, you automatically transform into Shadow. The battle is almost exactly like the previous one, except Castoth shoots more fireballs, and the fireballs move more quickly.
Lines of flames will go across the room. You can stand all the way at the bottom of the screen to avoid those flames. If you stand anywhere else, you will be in the line of fire.
Stay near a hand until it comes up, then hit it to get rid of it. After the hands are gone, wait for Castoth's eyes to open wide, then hit him between the eyes as many times as you can.
After a while, Castoth will start to shake and will then shoot lasers from the gem between his eyes. Run behind Castoth to avoid damage from the lasers, then when the hands reappear, repeat what you did before until Castoth dies.
After Dark Castoth
After the battle, heal and save in the Dark Space. Then go east and enter the door.
Go west and you find another door, but no Dark Space. Go into the door.
You will transform into Shadow again. Go upward to avoid getting pushed off by the wind. Viper can shoot a feather at you, and the feather then explodes into four. It can also shoot six feathers sideways at you. Stay near the bottom to avoid those attacks. Viper will also turn its head to the side and spits feathers/crystals, so move to the side to avoid this. Keep hitting Dark Viper until it dies.
After Dark Viper
Go back down to the Dark Space if you want to heal and save, then go back up, and go west to reach the exit.
In this room, there are tiles on the floor. Step into the center of the tiles and wait for a while. You will be sent to a higher floor. Go through the door in the new room.
Go east and you'll find another boss door.
Don't stand in a direct line from either of the vampires or you will be vulnerable to their fireball attacks. Stay away from the vampires if they put spinning energy balls around themselves. If the the two vampires float near each other and raise their capes, run away to avoid the large energy ball that they throw at you. To avoid damage, stay away from the vampires as much as possible, and only go close to attack as quickly as possible before running away again.
After Dark Vampires
You can't go back down the elevator that you used a moment ago, so go east and go through the door.
Go west and go into the door. Unfortunately there is no Dark Space that you can use before this next battle. Fortunately it is relatively easy to avoid damage in the next battle.
Dark Sand Fanger
Stay at the bottom of the screen and you will not be in the path of Sand Fanger's body. Hit Sand Fanger's head when you can.
After Dark Sand Fanger
Go west and go into the door. Go east and talk to the bird that looks like Dark Viper. After it drops you off, go west and into the door.
Go east and go into the door for another boss battle.
Dark Mummy Queen
Hit the mummy queen, then avoid the eight ghosts. Use the puddles or jump down to avoid the wandering ghosts. Hit the mummy queen when she reappears. Avoid the energy balls from her staff. During earthquakes, use Aura or go to the lower floor to reduce damage.
When her attack pattern changes, hit the non-flashing ghost to make her reappear, then hit her.
After Dark Mummy Queen
Go east and into the door, then go west and into the door. Wait for the vampire to come down and talk to him to go up, then go into the nearby door. Kara will talk to you. Go east to find a Dark Space. Heal up and save, then leave the Dark Space.
Talk to the spirit if you want to go back to Dao. You can do a sidequest if you have collected all 50 Red Jewels. Talk to Gem, who is standing between two houses in Dao. If you have 50 Red Jewels, Gem will take you to the Jeweler's Mansion. Talk to the floating soul in eastern Dao to return to the top of the Tower of Babel.
At the top of the Tower of Babel, enter the door next to the soul and the Dark Space. Go west and enter the door. Examine the skeleton. After the cutscene, talk to the souls, then talk to Olman. After that, talk to Kara. Watch the cutscene. The battle begins when you land on the comet.
Shadow now has the Firebird attack, which will shoot out from him across the screen. Hit the Comet with Firebird when the Comet opens its mouth. Stay in a corner and use Aura if a lightning bolt appears above you.
Break the blue bubbles with Firebird. Hold L or R to block the green orbs. When Dark Gaia opens her mouth, hit her repeatedly with Firebird, then move to the side to avoid her green laser, or use Aura to avoid the green laser.
Throughout the battle, you can stand below Dark Gaia and constantly use Firebird, only pausing to block the green orbs by holding L or R. The tricky part is getting back into position after avoiding the green laser without allowing the blue bubbles to hurt you.
Repeat this process until she dies.
Congratulations! You won!