Formation Change Gate
From Sonic Retro
Formation Change Gates have the appearance of light gates which are colour-coded according to each of the character types in the game: blue for the Speed Type, yellow for the Fly Type, and red for the Power Type. When the player passes through a Formation Change Gate, they will automatically switch to the assigned formation. For example, if either Sonic or Tails are leading Team Sonic when they pass through a red Formation Change Gate, Knuckles will become the leader.
The purpose of the Formation Change Gates is to automatically change the player's formation to a type that is best suited for an upcoming section in a stage. In some cases, there may be up to three Formation Change Gates of different colours in the same place, giving the player a choice on which formation they would like to use.