(EDIT: New version here: https://soundcloud.com/flaredragon-917007841/monsters-megalovania-v2)
(NOTE: Download link below)
A re-creation of Undertale's "Megalovania", with hints of other bosses' themes:
-A Long Time Ago/Undertale
-Battle Against a True Hero/Power of NEO (Undyne EX/Mettaton Neo)
-Heartache (Toriel)
-Bergentrückung (Asgore)
-Your Best Friend (Flowey)
-Nyeh Heh Heh/Bonetrousle (Papyrus)
-DETERMINATION

(All these themes, and Undertale, are owned by Toby Fox)
Download: http://puu.sh/qCTbB/108f3d7c1f.ogg (Right Click > "Save link as...")

Monsters' Megalovania

FlareDragon