Sunny prepared himself for battle before opening the gate of the Shadow Lantern.
He had no idea what would happen when it opened, after all. The mysterious archer had been able to send an arrow flying through the gate the last time — so, there was no guarantee that the unknown creature would not be able to escape the Shadow Realm itself if given an opportunity.
The battle could happen once Sunny passed through the Gate of Shadow, or it could happen right here, in the basement of the Brilliant Emporium. He had to be prepared either way.
Of course, there was also the possibility that nothing would happen.
A considerable amount of time had passed since Sunny's last attempt to explore the Shadow Realm. It was quite possible that the mysterious archer remained in the vicinity of the closed portal, waiting patiently for the door to open once again, but it was also possible that they had moved on.