Guard Door

Guard Door (ガードドア) is the first sub-boss of the Opening Stage from Mega Man X7. It is a security door with four blue crystals, one of which becomes red before the four orbs fire at Axl. Possessing a puzzle element, to open the door, Axl must shoot a red crystal three times in succession. If the wrong cores are shot before the door is completely open, the door closes again.