In Sonic Adventure 2 and Sonic Adventure 2: Battle, they appear once in every stage, and destroying one is worth 1000 points. If one doesn't shoot it quickly it will disappear and never be seen again unless the player dies, or the level is completed. In the Nintendo 3DS version of Sonic Generations, they appear in Radical Highway. If you use the homing attack on them before they disappear, they can be used to reach a higher path. There are apparently more than one of these in the stage, as one of the missions in mission mode is to destroy three of them within the time limit.