From the top right platform, jump to the left into the thorns, then climb the left wall.

Requires:

{"thornHits": 1},
{"or": [
  {"and": [
    "canUseIFrames",
    "canDash"
  ]},
  {"and": [
    {"tech": "canHorizontalDamageBoost"},
    "h_complexToCarryFlashSuit"
  ]},
  {"thornHits": 1}
]},
"canWallJump",
{"not": "f_DefeatedPhantoon"},
{"or": [
  "canRiskPermanentLossOfAccess",
  {"and": [
    "canDash",
    "canCarefulJump",
    {"disableEquipment": "HiJump"},
    {"or": [
      "canMoonwalk",
      "canTrickyJump"
    ]}
  ]},
  {"and": [
    "Gravity",
    "canDash"
  ]},
  {"and": [
    "canJumpIntoIBJ",
    "canBombHorizontally",
    "canTrickyJump"
  ]},
  {"and": [
    "Gravity",
    "canSpringBallJumpMidAir"
  ]},
  "canSpringFling",
  {"and": [
    "HiJump",
    "Gravity",
    "canInsaneJump"
  ]}
]}

Dev note: The canCarefulJump and Gravity are here, as with either of those, there is access across with or without f_DefeatedPhantoon.