Create an hardcore caracter (on PS3 by pressing
in the creation screen)
In hardcore mode, dying is permanent.
I haven't died yet (currently level 11 in hardcore ) so I'm not sure if this takes any room in the hero slots.(if anyone knows please comment)
The items gathered in normal mode aren't available in Hardcore mode. (in normal mode the items that you put in your stash are available for other hero's)
In game achievements are shared.