Back into the doorway on the left side of the room, and precisely jump under the floating platform. This requires a frame-perfect jump and frame-perfect release of jump. Samus must also aim down any time before reaching the left side of the floating platform; this can work as early as the first frame after jumping.

Requires:

{"doorUnlockedAtNode": 3},
"canInsaneMidAirMorph"

Exit condition:

"leaveWithMockball": {
  "remoteRunway": {
    "length": 5,
    "openEnd": 1,
    "steepDownTiles": 1
  },
  "landingRunway": {
    "length": 4,
    "openEnd": 1,
    "steepUpTiles": 1
  }
}

Unlocks doors:

{"types": ["ammo"], "requires": []}