This guide relates to the 'Rings of Mara' listed as a bonus item for the Imperial Edition of the Elder Scrolls Online:
RINGS OF MARA
Complete the Ritual of Mara with a friend and receive an experience bonus when you play together.
To achieve this there will need to be two players involved, but only one needs to posses the Imperial Edition bonus content; specifically an item called the 'Pledge of Mara'. This can only be completed at a 'Shrine of Mara'.
The Ring(s) are acquired after completing the 'Ritual of Mara'; the 'Pledge of Mara' is needed to initiate this action; and it must be done at a 'Shrine of Mara'.
To get the Ring(s) go to a 'Shrine of Mara'. If you are the one with the 'Pledge of Mara', place it in an available
Quick Slot; from which it can be used by pressing 'Q' presuming it is the active slottable item. Before using the 'Pledge of Mara' you must select the intended recipient, and then press 'Q'.
This video shows what you can expect to happen:
https://www.youtube.com/watch?v=ARupDwQ9OKU
The following link is helpful:
tamrieljournal.com/rings-of-mara-explained/
Baskin Robbins always finds out.
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eso.tamriel.org