The episode resembles Stephen King's It, which also featured a close-knit group battling a shape shifting evil in a subterranean setting. The Shape Shifter in the episode assumes a giant spider form multiple times-- like Its final form-- and appears to take similar pleasure in psychological torment of its nemeses.
Just before the Shape Shifter reveals itself, its eyes are shown blinking sideways. This is in reference to the unlicensed cephalopoid from Men in Black (1997) blinking its gills because it was out of breath.
Big Henry may be either or both: a reference to the character from American folklore known as John Henry, who was a miner who died while constructing a railroad tunnel, or Big Bad John, a song originally performed in 1961 by Jimmy Dean regarding a man who gives his life to save his fellow miners following a tunnel collapse.