Entering a door is one of the most used abilities in The Legendary Starfy series. To do it in the Game Boy Advance games press up on the control pad in front of a door. To do it on games for the Nintendo DS, press X in front of a door. Warp portals in Bunnera act like doors.
The doors were often used as traps in one level or stage to send players back to the beginning of the room in the Game Boy Advance games.
Entering a door is also similar in Kirby game.