Elden Souls

Stormfoot Catacombs in Limgrave becomes the Dark Soul Catacombs, full of arms, foes and a boss from Dark Souls (currently an unofficial dark souls boss), Dark Souls II and Dark Souls III. Everything is built from your own copies of the games on first launch: real models, textures, names, descriptions and icons.

The Merchant of Souls

Waiting at the catacombs' grace in Maughlin the Armourer's outfit, Sells 30 Dark Souls weapons and shields and 20 armor sets: Solaire's set and Sunlight Straight Sword, Havel's, Black Knight, Silver Knight, Catarina, Lothric Knight, Faraam, Heide Knight, Black Iron and more. Weapons take Ashes of War and infusions, and their damage is tuned to Elden Ring's scale.

Dark Souls foes

15 human soldiers in their real Dark Souls gear (Cleric and Balder Knights, Heide and Ruin Knights, Hollow and Royal Soldiers, Fallen Knights...) wielding the weapons from their own games, and dropping them.

Boss: Havel, Ornstein and Smough

A Dark Souls II-style gank fight behind the boss fog, with three health bars. Whoever dies last drops their soul: Soul of Havel the Rock, Soul of Ornstein or Soul of Smough. Use it for runes, or trade it with Enia at the Roundtable Hold for that boss's weapon or armor. Challenge of Ages at the grace lets you fight them again.

Needs

Elden Ring 2.7.1, Dark Souls Remastered, Dark Souls II: Scholar of the First Sin and Dark Souls III, all installed. The first Play builds the mashup from your games (several minutes; about 10 on a fast PC), then the game starts by itself. Single player, offline.