XX is the final Zone of Sonic Advance 2. Like the previous game's X-Zone, this is a single-Act Zone.
XX is essentially a "Boss Attack" level, because the player will have to fight all the bosses from the previous Zones in quick succession, from Leaf Forest's Egg Hammer Tank II to Egg Utopia's Egg Frog, which the player had just defeated. All of these boss machines have less durability than their initial battles, as each one of them takes 4 hits to be defeated (the cannon from Hot Crater's Egg Bomber Tank and the laser from Sky Canyon's Egg Saucer need only 2 hits to be destroyed). Though there are no Checkpoints, dying will restart the player from the boss they died at.
After getting rid of the Egg Frog, the exhausting run across the stage suddenly stops and the player faces the final boss of the Zone, Super Eggrobo Z. If the player finish this Zone with Sonic, Cream, Tails and Knuckles, and collects all the Chaos Emeralds using Sonic, they can advance to True Area 53, the real final Zone of the game, via the map screen. Otherwise, the normal ending plays and the game finishes right there.
Once the player reaches this Zone, the map screen's music will change to a remix.