• Arc Fatigue: Abe's journey to discover the truth about his existence. It goes on for several issues, with him waffling back and forth about his purpose and general navel-gazing with very little resolution. It takes the end of the Hell on Earth series to get a conclusive answer regarding his origins and he still expresses uncertainty about his goals.
  • Ensemble Darkhorse: Kate Corrigan was this back in Hellboy and gets bumped up to a lead role here. A few minor agents have built up enough reader love to make them the Dark Horses in this title, including Giarocco and Howards.
  • "Holy Shit!" Quotient:
    • Everything about "King Of Fear", the end of the Plague of Frogs cycle. Liz's vision of the future, the return of the sub-terranean race, who have allied themselves with the frogs, the return of the Black Flame and finally, the worldwide breakout of the Apocalypse, kicked off by the fact that Hellboy has just died over in his own book.
    • The finale of the Hell On Earth cycle. The Titans, Anum's fallen brethren who created the Ogdru Jahad, have risen from beneath Hell. Abe's coming back to Liz and the Bureau... but Iosif, Panya and Kate are dead. One of the Ogdru Jahad was loosed upon the world... but at the cost of his own life, Johann killed it! Oh, and Varvara's taken over Hell...
  • Magnificent Bastard: Memnan Saa again.
  • My Real Daddy: Mignola isn't shy about emphasizing the contributions of others to the BPRD series. In particular, he cites longtime series writer John Arcudi as the prime architect of many characters, including Ben Daimio. Some characters have also been "gifted" to others to write whenever they wish - BPRD agent Ashley Strode is Cameron Stewart's, and Simon Anders will only be written by Fabio Moon and Gabriel Ba.