Run and jump using SpeedBooster in the room below, with HiJump equipped. Bonk the door frame before passing through the transition, to cancel your horizontal momentum. After the transition, as you reach the wall, begin holding right. Land on the small platform below the top door.

Entrance condition:

{
  "comeInWithPlatformBelow": {
    "minHeight": 9,
    "maxHeight": 10,
    "maxLeftPosition": -38.5,
    "minRightPosition": -2
  },
  "comesThroughToilet": "any"
}

Requires:

"canCrossRoomJumpIntoWater"
"SpeedBooster"
"HiJump"

Dev note: This strat applies with Post Crocomire Jump Room or Crocomire's Room below.