Tad Stones says on the official Hellboy Animated Blog that the third film has not received the green light yet:
Meanwhile, no green light yet but when I have time I proceed as if we have one so that means organizing reference for my crew. As I’ve said previously, The Phantom Claw highlights the “mad scientist” side of Hellboy and nobody designs a mad scientist lab like Mike Mignola. This collage, along with several others, showcase the retro look to the equipment that Rasputin and his followers used to bring Hellboy to Earth. The images should not only help the design of background layouts but a variety of props too.
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Source: Tadd Stones