So basically all you want to do is make a new character, level it to 20, do all the HoW missions, start PoE lvl 28 and open the chest. No luck? start all over again untill u get it. I got my first Ghorn from doing this at my first try
Good luck
Edit: BUY IT FROM XUR RIGHT NOWW
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Just doing that once should take several hours...but then again you have to wait weeks just to get it in nightfall so whatever.