Atusa's Legs is a quest items in Divinity: Original Sin 2.
Location: Atusa's corpse
When you use Corpse Eater on it: Learn Fortify, and get some lore about about Atusa.
During dialog with Kniles the Flenser: Pacifies him. Fane can acquire the Face Ripper.
You can feed it to Buddy; it will make him upset.
- As of the most recent patch, eating the leg no longer grants a skill.
Should you hold onto the leg while either within the fort or even after escaping it, you can find yourself in the sewers; also called "Kniles's Playground." Within' you will meet a Magister character by the name of "Kniles the Flenser" who will begin a dialog and quite creepily sniff out the leg still in your bag, and demand that you hand it over to him. If Fane is in your party, he’ll ask for Kniles’ face ripper in exchange.
similar to garvans head, start the dialogue with fane, at the moment where you are to hand over the leg, have your elf eat it. they learn the lore, and kniles still gives fane the face-ripper. side note: i got the lore but not fortify.
Where is her corpse
Ate it as Sebille and learned First Aid
just ate it, didn't learn fortify...
Atusa's Leg, with Fane in the group, can be traded to Kniles the Flenser just upstairs from the Fort Joy prison (in the bloody area with the body parts, monks and caged flesh golems). In return, you are given the Face Ripper, Fane's quest item, and free pass to simply leave the fort.
Alternatively, consuming the leg as an elf (or as Fane, disguised as an elf) grants you the Geomancy spell Fortify, and a bit of insight in Atusa's life.