Sylas was shocked by the sudden appearance of the portal because he had sensed nothing at all. There was no rush of Aether or wild fluctuation. In one moment, there was nothing. And in the next instant, it had poofed into existence.
'This is bad.'
It wasn't hard to imagine all the potential problems that could pop out because of this alone. Silent Portals that led to who knows where might not mean death, but if he was thrown off course again and again, not to mention forced to fight a bunch of unnecessary battles, he wouldn't end up getting anything he wanted out of this experience.
'Clear the Mountain of Giza Dungeon…'
That was supposed to be his task, but there was no Dungeon to be seen. In fact, judging by the situation outside, it didn't feel like there was any Dungeon nearby at all. Otherwise, there would probably be more than just the Glass Monkey wreaking havoc.