This reminds me of the show-down between Seymour & Audrey 2 from "Little Show of Horrors."
Speaking of which, if there was a way that the Once-ler was having a showdown with his greed-sin (like what happened in "American McGee's Alice" when Alice had to face the Queen of Hearts, who is actually her inner-insanity/warth);
Doesn't Audret 2's song, "Mean, Green Mother F- From Outer Space" match Greed-Ler very well? [link]
And can you imagine Greed-Ler singing that to Once-Ler (though the fowl language would be inappropriate )?