There’s a new bug on the PTR and in the Reaper of Souls beta that allows a player to repeatedly exploit the guaranteed legendary drop from Act Bosses. A fan sort of brought it up on the forums and got a reply from a Blue who didn’t know about the bug yet. (But I bet they do by now.)
It says “Restarting will give you bonus rewards for completing quests!” but that doesn’t include the guaranteed legendary drop the first time you kill an act boss. I think it should reset the boss drop. There should be a way to get a guaranteed legendary drop in the game other than leveling a whole new character.
Grimiku: Currently the game is designed to only give players a Legendary item the first time they kill a major boss, but you should find a Legendary item with some level of frequency after that. We recently made some changes to our system to help ensure players are finding those items. For reference, you can read a little more about that system in this post from Travis Day.
The guy in the OP doesn’t quite get it, but some of the guys in our INC guild were talking about this today in guild chat, and apparently it’s quite easy to do. If you do a whole Act in sequence (not just leaping to the last quest), in Story Mode, you will get a legendary drop guaranteed from each Act Boss, the first time you kill it with each character. The bug now is that if you reset your quest progress, just restarting at the beginning of that act or an earlier act, you’ll get the guaranteed legendary again from that Act Boss. (I haven’t tested this myself because RoS, so if I have a detail wrong hit it in comments and I’ll correct.)
What keeps this from being a real exploit is that it only works up through lvl 59. Once you hit lvl 60 the guaranteed drop goes away, and that pretty much keeps it from being of any use in level 70 world of Reaper of Souls. Legendaries of level 55-59 are potentially pretty useful on the PTR though.