Grapple Supersink
From A complete guide to Super Metroid speedrunning
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If Grapple is canceled during a grapple swing appropriately, so Samus has vertical speed greater than her usual cap, then her fall speed becomes effectively uncapped. Via appropriate movement (using angles and wiggling), this speed can be effectively and increased, to clip ridiculous far downward.
I am unsure how easy any of this is to do RTA.
