Grapple to the second Grapple block from the bottom (the one partially underwater), jump off from it, morph, and press against the wall to the right. Unmorph slightly before the peak of the jump (a 3-frame window), then immediately use grapple (a 2-frame window) to get stuck standing a pixel inside the second Grapple block. Then jump (to force crouch), angle down, and grapple. Press jump to get a good bounce off the wall at the bottom of the swing, making it possible to swing up to close the door. To minimize lag, when grapple is extended horizontally release all inputs other than shot/grapple; there will still be a bit of unavoidable lag while Grapple is initially extending. Try to get a good first bounce; otherwise heavy lag may be difficult to avoid, and it may be better to retry from the beginning. Retract Grapple while approaching the door. Samus should come to a stop about a tile in front of the door (at horizontal position 1753). Press right and then left, and Samus will fall through the floor. Back to the right within the air pocket, then jump and use Grapple diagonally up against the second Grapple block from the bottom, near its top. Samus should be pushed most of the way inside the wall; if not, morph and roll out to try again. Once in position far enough inside the wall, grapple diagonally up again to be pushed into the transition.