Good news! The Shovel Knight Amiibo has already sold out forever. It hasn't even gone on sale yet, and there are no pre-orders for it yet, but you've already forever missed your chance to get it. Shame, too, since this is the first time an Amiibo has unlocked somepthing VIABLE for a game.
But really, while I think this is probably the coolest features to come with an Amiibo yet, it just...doesn't seem fair for something like Co-op to be locked behind an Amiibo, of all things. But hey, they'll probably make the regular version and the smash Bros. version, so it might be twice as not-rare, which would still be very, very rare.