Something bad.
Does it take more than that to make an interesting villain? Arguably, no. A lot of the fun of Hellboy: Sword of Storms is the variety of antagonists. Vampire heads, the Spider Lady and the turtle-shelled kappa all wanted to do Hellboy harm. Yeah, they were working for other villains, but within their episodes they mostly wanted Hellboy dead. Did they have personalities? Sure... well, not certain about the kappa, but the rest were mostly given a unique feel by the actors who played them.
In Hellboy: Blood and Iron Erzsebet, the Blood Countess, is after youth and revenge against Professor Broom. Her viciousness and her back story make her more interesting than the monsters of the previous movie. She's not working for someone else, she is her own master. Definitely a step up, I think. The more formidable the adversary, the bigger challenge to our heroes. It is her nature that makes the movie so much darker in tone than the first.
The villains of Hellboy: The Phantom Claw often take the center stage. You only see Kronen and Ilsa in a flashback to Hellboy's summoning but Rasputin, Von Klempt, Kriegaffes, Roderick Zinco and a Frankenstein monster army all have major parts to play. Beyond giving each a personality that an actor can embroider, each has a different agenda and some of those are in conflict.
Before I go on, I guess I have to point out that this discussion of story may include minor spoilers but nothing that isn't already printed in the Hellboy books.
Rasputin is the charismatic manipulator, we see how he seduces and deceives people into doing his will. He is the zealot with a grand vision who demands that people put aside everything for his goal. If your wealth will help the cause, he'll take it - or rather convince you to donate it. If your family is a distraction, they will be removed. Rasputin is an interesting antagonist because he believes he is doing the greater good, bringing paradise to Earth. The fact that it requires scouring the present planet of all life doesn't seem to bother him. He is also an intelligent villain who is thinking well beyond the others.
Von Klempt is the put upon villain. He has his own plan, to create an army of dead guys - you see them in Conqueror Worm. To him, connecting dead body parts to robots makes sense. As Mike Mignola told me, "At least you can rob banks with them," which, I suppose, is as good a gauge as any to determine the practicality of any villain's plan. There's an amusing side to Von Klempt's situation - whenever he gets close to pulling off his plan, Rasputin shows up and turns his resources toward his "end the world to birth a new one" obsession. I hope that he'll provide some laughs but he is by no means a comic relief character.
Roderick Zinco is a billionaire who joined a secret society, THE WOTANIC CIRCLE, in order to gain access to the equipment that brought Hellboy into the world, equipment that promises a limitless source of energy. Zinco's journey to Hell through the picture is the classic cautionary horror story of "be careful what you wish for." He is the canvas upon which Rasputin's evil is traced.
Kriegaffe, the "war ape," is muscle but his relationship with Von Klempt might make you a touch sympathetic, even while he's using a zombie body as a club to beat you.
These bad buys should give The Phantom Claw a completely different feel from the first two movies. They are also part of the reason that Liz and Abe won't be along. We need the time to make them richer and paint a more detailed picture of their relationship to Hellboy. And how their stories are bound to Hellboy's origin... and destiny. --Tad