In Full Randomizer, you'll often want to check the Billy Mays Room before picking up Gravity Suit. To get on top of the invisible platform in the Boulder Room, jump into the door transition. You may need to walljump off of the side of the invisible platform if you have Hi-Jump Boots or if you jump into the door very early.

After checking the items, you can make it through the door just by firing an angle-down shot and running through, but the timing of that shot can be tough. Otherwise, you'll end up in the water. To get out, you can do a crouch-jump downgrab when the water level is at its highest, as shown in the video. Alternatively, you can run and walljump below the door when the water is at its lowest.