Disclaimer: Dr. Horrible is copyrighted, trademarked, and so forth by people like Joss Whedon and Mutant Enemy, and not by me. I make no money from any of these images.
If you use them, credit and a reply post would be nice. They're not required, as long as you don't actually pretend you made these yourself or something.
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Spoilers for all three acts of Dr. Horrible. )