I'm so below the casket, ragged pulse of the maggots

from Tech N9ne (Ft. Krizz Kaliko) – Low Lyrics on Rap Genius

Meaning

Comparing himself to being a corpse that can feels the maggots shifting under him. Possibly a reference to the song “Pulse of the Maggots” by Slipknot. He feels lifeless, tortured, disinterested.
http://www.youtube.com/watch?v=_glgZAlS490 Slipknot uses clown masks and had a heavy emphasis on rapping in the 90s: Tech is a fan

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