JCoxeye's Leitmotif Index:
'Another Medium'

Summary

'Another Medium' is primarily used as the theme of Hotland.
It's split into two parts:

('Another Medium' A and B, as heard in Another Medium)

The melody also has an accompanying ostinato, which is also heard elsewhere in the soundtrack:

('Another Medium (Ostinato)' as heard in Another Medium)

This ostinato is also debatably heard in An Ending, Don't Give Up, Respite, and (even more debatably) Reunited. A proper analysis of those is forthcoming.

In CORE, Death By Glamour, and Bring It In, Guys!, 'Another Medium' is accompanied by the CORE's own leitmotif, 'CORE':

('CORE' as heard in CORE )

Finally, it should be noted that the 'Another Medium (Ostinato)' originates from a prior Toby Fox composition, Patient, as discussed on the page 'On the Origins of Undertale and Deltarune's Leitmotifs'.