User blog comment:ZXdemonXZ/Hardmode bosses spawn automaticly/@comment-5167837-20131112091830

This blog has been answered, but just for additional information, if you see "This is going to be a terrible night." (The Twins),  "You feel vibrations coming from deep below" (Destroyer)and  "You feel the air get colder around you." (Skeletron Prime) when night starts, be prepared!