Omnilovania appears to be a fan-made musical mashup that combines multiple arrangements and versions of "Megalovania", the iconic boss battle theme from Toby Fox's indie game Undertale. Since the game's release in 2015, Megalovania has become an internet sensation, inspiring countless covers, remixes, and orchestral arrangements across YouTube and music sharing platforms. This particular version seems to be a collaborative effort to combine many of these variations into one comprehensive "omnibus" arrangement.