Dampyr #104 (2008) pages 91-92: To save my friends

(Samael's scrying mirror shows Tesla that Kurjak is in Sonderling's "Witches Sabbath" painting, being clawed by a hag.) “Aaahhh!”

“Kurjak! Emil! What are they doing to him? Is this another one of your tricks, Samael?”

“It's reality. Kurjak is now a prisoner of Sonderling's magical workshop and his marvelous creations. You lured him there.”

“Me?”

“Lady Druj took on your appearance, just as she took on Hanneke's to deceive you. She works for Nergal. And I decided to go along with her plans, too, because in exchange I could have you. I want just one more night of love with you, my vampire warrior. Then I will free Kurjak... even against Nergal's wishes.”

“You're lying! Because you know full well that making love to you again could make me your slave forever.”

“That's very likely, but... you'd save your friends. And I'm not just referring to Kurjak and Harlan's girlfriend, whom you might prefer dead. Look again, my friend.”

(They look into the mirror again.) “Those ugly mugs... I saw them in another of Sinistrari's paintings. Who are they?”

“Two infernal princes: Alastor, executioner of hell, with his soul-sucking sword, and Dagon, prince of the humid abyss, lord of diseased blood. They're waiting in the tunnel for clueless Harlan Draka, who is in Nergal's slaughterhouse in Prague. And not even a Dampyr can do anything against two infernal princes. Although I believe they'll limit themselves to capturing him and converting him to evil... after a few centuries of torture, as Nergal desires.”

“They won't succeed. Are you blind, Samael? Caleb Lost is with him... And Caleb is more powerful than those two losers.”

“That remains to be seen, but Duke Nergal is cunning and has thought of this too... observe carefully.”

(Harlan) “Nergal can't be here. I'd sense him.”

(Caleb) “But there's someone else. I have a feeling that...”

That shimmer around Caleb's legs in the last panel is not spilled paint. But what is it?