Andariel returns in Diablo 4’s Season 4 update, and taking her on is a tall order. You should be packing some excellent gear and be at or above level 100 to take on Echo of Andariel. But before you can even attempt it, you’re going to need how to get where she can be summoned: Hanged Man’s Hall.
Getting right into the meat of what you need to know, the Hanged Man’s Hall lair is found East of Tarsarak in Kehjistan. It’s not all that far. Here’s a picture:
Working backwards, in order to summon the Echo of Andariel, you’re going to need two Pincushioned Dolls and two Sandscorched Shackles. Pincushioned Dolls are gained from The Beast in the Ice and Sandscorched Shackles are dropped by Lord Zir. These are endgame bosses if that isn’t already clear. You need to fight them in World Tier 4.
You’ve probably learned this, but the Pincushioned Dolls and Sanscorched Shackles you use in the summon will be consumed.
Andariel is pretty analogous to her brother Duriel. That’s in terms of power level, but also in the loot that gets dropped.
Also note that you can now fight Tormented versions of the bosses, if you feel prepared. These are level 200 versions that have better chances at rare loot. In order to summon the tormented version, you need Stygian Stones, as well as six Sandsorched Shackles and six Pincushioned Dolls. Good hunting.
