Run and spin jump to the left through the transition with as much horiziontal speed as possible, without bonking the door frame. Hold left through the transition to avoid the fish and land on the platform to the left. With limited runway, this may require a very precise jump. Then reach the platform above either using a crouch-jump down-grab or by freezing the fish.

Entrance condition:

{
  "comeInWithPlatformBelow": {
    "maxHeight": 6,
    "maxLeftPosition": -0.5,
    "minRightPosition": 2.5
  },
  "comesThroughToilet": "yes"
}

Requires:

"canCrossRoomJumpIntoWater"
"canInsaneJump"
{
  "or": [
    "h_canCrouchJumpDownGrab",
    "canUseFrozenEnemies"
  ]
}