AC Valhalla Sisters of Lerion are some of the game's toughest bosses. You'll need to defeat them to get parts of Thor's Armor. Here's where to find the Sisters of Lerion and how to beat them.
AC Valhalla Sisters of Lerion: Where to Find and How to Beat
Each of the three Sisters will wait for you in a decayed arena. The locations are marked with a desecrated corps. Upon defeat, they will also each drop their Dagger and a piece of Thor's armor.
Goneril - 90
Goneril is found in Spalda Fen at Grantebridgescire. She fights with twin blades and can deal heavy damage quickly if you're not careful. Goneril is overleveled for the region, so be careful if you find her early. Use weapons with more reach in this fight.
Her other attacks include releasing poisonous gas, teleporting and summoning phantoms. Defeat her for Thor's Battle Breeches and Goneril's Dagger.
Regan - 160
Regan will be waiting for you at Walsham Grag in East Anglia. Like Goneril, she also rushes with twin blades and phantom summons. She'll use fire instead of poison and can use parries against you. Get around this with your own unblockable attacks. She drops Thor's Battle Plate and Regan's Dagger.
Coredelia - Level 340
The final and strongest Sister is also at East Anglia, in Berkelow Bog. The strongest of the Sisters of Lerion, she'll attack you with a variety of quick and powerful strikes. She will summon several phantoms to attack you, which may very well kill you. The trick to this is to stagger her before she can summon them. Once she's down, you'll get Thor's Battle Gauntlets and Cordelia's Dagger.
With all three daggers in tow, you can return to the Lerion Estate and open the treasure horde containing Thor's Helmet.