I'll always pick the archer
I had and have a wholly unsatisfied desire to shoot well with a bow. -J.R.R. Tolkien
It says monster sctivates, but what happens if there's no active player?
How would there not be an active player? Whoever was the party leader would be the active player and take whatever happens from the monster activation. If the party leader is somehow currently knocked out, just proceed to the next player. I'm not sure exactly what the card says, but treat monsters activating and targeting in the same way as you always do.