Place Power Bombs to kill the Metroids. By hitting the first Rinka, all of the Metroids (on a similar vertical height to the Power Bomb) will be damaged.

Requires:

{"enemyKill": {
  "enemies": [["Metroid", "Metroid", "Metroid"]],
  "explicitWeapons": ["PowerBombPeriphery"]
}},
{"or": [
  "canTrickyJump",
  {"ammo": {"type": "PowerBomb", "count": 2}}
]},
{"metroidFrames": 200}

Sets flags: f_KilledMetroidRoom3

Dev note: Using 1 pack of PBs isn't intuitive as a way to kill 3 metroids without grouping them. Killing the first Metroid happens to group the other two nearby, and when jumping close to them they derp around.