There are no longer any active military or research campaigns in the Eris region – it is overrun. Long evacuated Corpus and Grineer vessels drift aimlessly in orbit, slowly being devoured by the techno-organic parasite known as the “Infestation”. What remains is a twisted graveyard of partially-digested ships that are disfigured versions of their original forms... Abandoned, but not unoccupied.
Eris also has the unique distinction of having two unique Assassination targets: Mutalist Alad V and the Jordas Golem, each occupying their own nodes and having their own unique missions. While Phobos was the first planet to have two Assassination targets with the team-up of Captain Vor and Lech Kril, unlike with Eris both bosses are found on the same mission, and the pair are considered a single Assassination target.
Interestingly, as Mutalist Alad V requires a key to access, and "The Jordas Golem Assassination" has the Jordas Precept as a prerequisite, unless the player has the components for Mutalist Alad V's key or the Jordas precept quest completed, there are no available assassination missions available on Eris.
The two individual boss-fights on Eris make it the first planet in the game on which two Warframes are dropped.
Prior to Update 11.0, Eris's (and Europa's) description read: "The Infested are spreading throughout the Orokin Derelicts in this region". This implied that at least some of the Orokin Derelicts are located here.
The Infested have further expanded on Eris! Introducing new Infested Rescue mission with new stakes! Also on Eris are brand new Defense and Mobile Defense maps, fight through Infested Corpus ships to defend your objectives!
With the return of Infested comes the return of Mutagen as a Rare drop to Eris!