In Season 4, Blizzard added another level of bosses to the Boss Ladder called Tormented Echoes.
Tormented Echoes are level 200 bosses.
How to summon Tormented Echoes
These super hard bosses are summoned with Sygian Stones.
Where do you get Stygian Stones?
Stygian Stones are acquired from the endgame content called The Pit.
Tormented Echoes Drops
All items dropped are item level 925.
Defeating your first Tormented Echo drops one Resplendent Spark as a first-time reward (account bound).