He could feel the portal forming, feel the foul energies swirling as they coalesced into a gateway from one world to the next, allowing the demon passage. He could feel the demon too, though only distantly now, as the portal was not yet fully formed and his sense of the other side was clouded. He'd spotted the two on one of the impossibly tall building a moment earlier, and wondered what it was they were going to do from up there. They couldn't simply be bystanders, not armed and clad the way they were, and yet they'd chosen a vantage point dozens of levels taller than their enemy was going to be. Perhaps they possessed ranged weapons or magic and were planning to rain their power down on it. 

Regardless, Ahven himself had chosen a much shorter point to make his perch, a mere six floors from the ground and on the opposite side of the portal from the other two. For now, he ignored them and focused instead on the portal and its hellish cargo, waiting behind the pane of sheer glass for the monster to make its appearance.