21. Who ended up dying in the end, allowing Dr. Horrible to join the Evil League of Evil?
From Quiz Dr. Horrible's Sing-Along Blog
Answer:
Penny
When Dr. Horrible was punched, he dropped his Death Ray, causing it to malfunction. Captain Hammer picked up the weapon and tried to shoot Dr. Horrible point blank, but the Death Ray exploded, knocking Captain Hammer back. Dr. Horrible, miraculously, was unscathed. Captain Hammer began to cry, feeling pain for the first time in his life, and ran off looking for his mom (or someone maternal).
Dr. Horrible got up and looked around, and noticed that Penny had been impaled by shrapnel from the Death Ray. Dr. Horrible carried her to the stretcher while the song "Everything You Ever" played, but she was already dead by that time.
The closing montage showed Dr. Horrible robbing a bank, hosting a party for his evil friends, and finally joining the Evil League of Evil. The very last shot has Dr. Horrible saying he did not feel a thing (despite his success).