Anyone play Rivals for Catan? Questions about the arsonist and discard pile

There isn't much explaining what GOES in the discard pile and when its used. Can somone explain what its for/When its used? The game states that you can only see the face up card? Whats the reason for this?

And lastly, can I theoretically play the arsonist EVERY single turn if I pay the resources to search the Era of Termoil deck for the arsonist every hand?