Questions about the gameplay of Heroes 6.

Since I haven't played Inferno much, I can only say that you sometimes encounter a building on the map that provides a worm for one battle. And I think it even gives out worms every week (though I might be wrong). Also, there's a building in Inferno, but I haven't built it yet. ^_^
I didn't realize right away that you could build alternative buildings in castles if you click on the double-headed arrow.