Timer Balloons are important collectibles in the Goop series and they allow Goop to replay levels as a time trial in the first Goop game: Goop's World. They are pink balloons with a white letter "T" on them.
Timer Balloons appear at the beginning of a stage after you complete all of its challenges. After returning to a completed stage, players can pop the balloon and activate the time trial, prompting them to have to reach the end of the stage in the short time limit. Completing this gains the player another Magic Opal.