Which Paper Mario game features a turn-based battle system with an audience that throws items?

The Paper Mario game featuring a turn-based battle system with an audience that throws items is Paper Mario: The Thousand-Year Door. Battles take place like stage performances, with spectators reacting to Mario's attacks, mistakes, and special moves.

The audience can cheer and help refill Mario's Star Power when he performs well. If the player executes attacks impressively, spectators may throw helpful objects such as mushrooms toward the stage. Poor performance can cause the audience to leave or throw harmful objects at Mario instead, adding risk to the battle system.

The audience begins with a maximum size of 50 and can grow to as many as 200 as Mario levels up. This mechanic is one reason the GameCube title is often remembered for combining traditional role-playing elements with theatrical presentation. The later Paper Mario games in the options changed the battle format and did not use this same audience system.