Altar Emerald (アルターエメラルド,Arutā Emerarudo?) is the eighth Zone in Sonic Advance 3, following Chaos Angel. Altar Emerald is a boss level, featuring a battle with Gemerl and then a second battle with a robot called Hyper Eggrobo. If all seven Chaos Emeralds have been collected and Sonic is the leading character, Altar Emerald is followed by the true final level of the game, Nonaggression.
The first boss of Altar Emerald is Gemerl. During this battle, Gemerl will attack the player with full-body charges, missile barrages in two different formations, or launch surprise attacks by teleporting into the middle of the field and then charge at the player. To damage Gemerl, the player must attack him when he lets his guard down. After four hits he will be defeated.
The second and last boss of Altar Emerald is the Hyper Eggrobo, piloted by Dr. Eggman. To damage this boss, the player must attack Eggman's cockpit. During this boss battle, the Hyper Eggrobo will uses the following attacks.
Slam Hand: Slam hand is where hit slams and pushes the ground down where the player can then jump on the hand to attack Eggman.
Punching: Punching is where the Hyper Eggrobo pulls its hands back and attempts to punch the character.
Pong: Pong is where the Hyper Eggrobo pulls hands bounce back three red balls which can be jumped on and attack Eggman.
Grab: Grab is where the Hyper Eggrobo's hands attempt to grab the player. If he does, then it slams the player on the ground.
After Eggman defeated, all the characters come to the Altar to celebrate and Omochao takes a picture, then the credits roll. However, if the player has collected all of the Chaos Emeralds and is playing as Sonic, then the player will move to the secret final boss, Ultimate Gemerl, in Nonaggression.
The Act's theme song is a remix of Holy Summit's music, and in turn, a remix of Tikal's theme song.
The zone mechanics are similar to Death Egg Zone, as both of them are only a sub-boss and then the final boss.