Talk:NPC/@comment-5442791-20150703134000/@comment-15695624-20150709030455

I found him (the Skeleton Merchant) in one of my fishing areas in the cavern layer. I got a red and blue Counterweight from him, then I let him get off screen and he despawned.

While he is on the screen, no other monsters will spawn. I haven't tested this during a Blood Moon - that would likely override the spawning prevention.