The Organical Fortress is the stage 5 in Gradius Gaiden. Your interesting dogfight opponent is Gau, originally from Life Force. At any rate, three of them show up, firing triple lasers and destroyable eyeball missiles. They aren't particularly tough, so blast them and move on. The living floor and ceiling tend in this level begin to get narrow, and occasionally move erratically. Get rid of the green flapping enemies as soon as possible, as they're often blocking the path. Later on some green and purple bulbs will sprout tendrils that connect to the floor and ceiling. You can attack the bulbs directly if you wish, but a better tactic is to disconnect it from either the floor or the ceiling, sending it flying in the opposite direction and destroying it. The purple blobs that appear at the sa