Hardmode is like a different game developed after Terraria became an unexpected smash hit. The game might as well have a link to the official wiki on the UI once hardmode activates, because it seems to be assumed that you're using it, and the Guide's only line should be, "You're using the wiki right? You're playing Terraria hardmode now. It might as well be Terraria 2 for how much it resembles pre-hardmode."