'With a Tarnished's Furled Finger, you can leave a gold summon sign. This sign will appear in other players' worlds and allow them to summon you as a Furled Finger for cooperative multiplayer.' The Tarnished's Furled Finger is the canon's diegetic justification for cooperative multiplayer : a small, gold-clenched-fist totem that, when laid upon the ground at a Site of Lost Grace, leaves a sign in the worlds of OTHER Tarnished, in OTHER versions of the Lands Between. The other Tarnished can summon you to fight alongside them. Your hand, your specific hand with its specific weapons and spells, will appear in their world to defend a stretch of road that has perhaps been defended a thousand times before by other versions of yourself.

'Cooperative multiplayer will begin once you have been summoned by a player from another world. You will take the role of an ally (Furled Finger) and your objective is to defeat the area boss.' The canon's metaphysics around the Tarnished's Furled Finger are richer than the multiplayer-frame suggests. Every Tarnished hears the call of grace. Every Tarnished is a separate person on a separate path. But the Furled Finger creates a back-channel : a way for two such Tarnished to briefly cohabit one world's surface, fight one boss together, and then dissolve. The lore-frame is that grace itself can lend hands across the fog. The mechanic-frame is that you are summoned. They are the same thing.