Nyarlathotep

Composed by Nato, the song extends the Cthulhu Mythos naming theme already established by Yog-Sothoth and Shub Niggurath, and joins the Outer God series. Nato initially announced it as the final entry in that series, but Pump It Up PHOENIX later added a fourth Outer God track, Ghroth. The fast piano passages in the back half resemble Nihilism, another piece by the same composer. On January 31, 2019, Nato released a self-made arrangement called the Transcore Mix on YouTube, set slightly slower than the original at 185 BPM.

Unlike the earlier songs in the series, whose visuals were handled by YSJ, the BGA was produced by Lyrebird Ferdinant. It is packed with hints and Easter eggs, and in keeping with the entity that lends the song its name, the BGA breaks the fourth wall. Among its touches is an error screen styled after old operating-system crash pages that obliquely references other Nato compositions and seems to address the player directly.

A defining trait is that every chart is built tougher than its peers at the same level. In Single it appears as S13, S17, S18, S21, and S23, and in Double as D17, D20, D23, and D25; apart from the D25, all of the Double charts are Half-Double charts confined to the six central panels. The S18 opens the 18-21-23 progression inherited from Yog-Sothoth but plays harder than its predecessor, capped by a lengthy 16th-note run that can drain weaker players. The song also has Short Cut charts: an S22 and a D24, the latter the first-ever Short Cut to reach level 24. The S22 Short Cut is notorious for the "sewing-machine" hold-and-tap pattern near the end and for a quirky phenomenon: many players deliberately pick it to bow out when they are down to a single heart.