The trio entering the Desire Room in Space Face. What does Edd turn out to want the most? A felt-tip pen so he can have fun drawing stuff. Considering this was the final toon where the character was (for the most part) voiced by the real Edd Gould, it winds up being a very appropriate, heartfelt send-off: a tribute to Mr. Gould and a celebration of his life, who he was, and what he did. The upbeat, cheerful music only adds to the effect.
Edd (creator/animator/his Author Avatar's voice actor) has passed away, so the series will die? Nope, it will be continued by his real life friends (Thomas Ridgewell (Tom's VA and ASDFmovie creator) as head writer and producer and Paul ter Voorde as animator).