Turtle Shell is one of the multiplayer stages for the Battle mode in Sonic Heroes. When playing all three stages of Team Battle, this is the third and last stage in order if each player has won one stage, hence Turtle Shell is the deciding round for the winner of Battle.
The two teams battle against each other above an arena above a large turtle's shell (hence the name) which takes on the scenery from the stage Ocean Palace of single player mode. The arena the turtle carries is a flat, fairly-rectangular piece of ruins with green and dark green tiles styled in a checkerboard-pattern. A fair few plants grow on the arena such as tiny shrubs and palm trees.
At both ends a three-lighted spring rests on the ground, which grants the player a fully filled Team Blast Gauge, giving the opportunity for the player to launch a Team Blast attack on the opposing team. Early through the fight, round, floating Item Boxes containing Power Cores to enhance the character's level, giving their attacks a bit more powerful and able to take down the opposing team quicker. These item boxes will float across the stage before disappearing so either team needs to be quick to touch them in order to obtain the Power Core.
The player can also knock the opposing team's character(s) off of the sides of the stage, preventing the leader character that got knocked off from being used. However, any lost character(s) can be brought back by using the team's Team Blast should they successfully fill their Team Blast Gauge.
The winner in this stage is whichever team can force the opposing team off the stage first.