Mega Man X7

Towards the end of Vanishing Gungaroo's stage, you must fight a series of enemy ride armor in a room with pillars. Climb one of these pillars and jump across them to reach an extra tank. If you've brought a ride armor into this room, you can leave it in the middle of the room and fight the bad guys on foot. After beating the last enemy armor, you will automatically encounter Gungaroo. As long as you leave your ride armor within the battle perimeter, you can use it against the boss when the battle begins.

On the character select screen, hold SELECT when choosing X. He will now have all his armor.

Rescue 65 reploids to be able to play as X.