Mignola, M., Stewart, D., & Robins, C. (2021). Hellboy universe essentials: Plague of frogs (First edition.). Dark Horse Books.
शिकागो शैली (17वां संस्करण) प्रशस्ति पत्रMignola, Mike, Dave Stewart, और Clem Robins. Hellboy Universe Essentials: Plague of Frogs. First edition. Milwaukie, OR: Dark Horse Books, 2021.
एमएलए (8वां संस्करण) प्रशस्ति पत्रMignola, Mike, et al. Hellboy Universe Essentials: Plague of Frogs. First edition. Dark Horse Books, 2021.
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