Tribute
Tribute is Tenacious D's most famous and most perfectly constructed song — a comedic epic about the greatest song in the world whose central joke is that the song never actually plays the greatest song in the world. Its dynamic structure, from quiet acoustic opening to full arena-rock climax, demonstrates the duo's ability to write a genuinely great song about writing a song they're not going to play.
Tribute describes an encounter with a demon who demands the duo play the greatest song in the world or forfeit their souls — they do so brilliantly, but the song you're hearing is merely a tribute to it, not the thing itself. The joke works because the song is genuinely excellent anyway.