Interesting, I didn't know it was infernal as I never romanced Astarion myself ^^
This makes me think what if Cazador and Raphael are actually in league with one another and it was actually Raphael who told Cazador on how to inscribe the thing on Astarion's back. Which then could explain why Raphael literally shows up out of nowhere directly at our camp, precisely because Cazador told him that Astarion went missing.
Raphael is definitely playing an intricate game here. Because he couldn't care less about the tadpole, or us in particular for that matter. He wants something else, perhaps even the artifact. Because so far absolutely nobody cares about us, everyone wants the artifact.
Also Raphael saves us from Priestess Gut by sending the female dwarf assassin. My guess is he wants us to get somewhere in particular. It is a question of location, not time as he tried to imply.
