Standing on the platform in the room below, crouch jump up and press right against the door frame through the transition.

Entrance condition:

{
  "comeInWithPlatformBelow": {
    "minHeight": 10,
    "maxHeight": 10,
    "maxLeftPosition": 1,
    "minRightPosition": 2
  },
  "comesThroughToilet": "no"
}

Requires:

"canCrossRoomJumpIntoWater"
"HiJump"
"canCrouchJump"

Dev note: This strat only works for platforms that are 10 tiles below the door transition (Crocomire's Room). It could be done for a platform 9 tiles below the door transition, but this would require a momentum-conserving turn-around; it is easier to just do a standing jump or spin jump in that case instead of crouch jumping.