Please tell me all the doors are not like this.
Trap Door, also known as TrapDoor or Assult Door, is an enemy in Final Fantasy IV. The only way they can be fought is by pressing the action button on a locked door at the Sealed Cave and can never be fought as a random encounter. They are far stronger than the other enemies in the area.
Trap Door will lock on to one of the characters with Target, then cast Ninth Dimension on the next turn, instantly killing the targeted character. An easy way to defeat the Trap Doors is to wait for it to cast Target, then have Rosa cast Reflect on the targeted character. When the Trap Door casts Ninth Dimension, it will kill itself instead. This works in all versions of the game.