Rings of Brighthearth
Three Rings for the Elven-Kings
Artifact
Whenever you activate an ability, if it isn't a mana ability, you may pay 
. If you do, copy that ability. You may choose new targets for the copy.
All that has been wrought by those who wield the Three will turn to their undoing, and their minds and hearts will become revealed to Sauron, if he regains the One.
Illustrated by
Tales of Middle-earth Commander#352MythicEnglishLegality
Rulings
An activated mana ability is one that produces mana as it resolves, not one that costs mana to activate.
You can’t pay more than once for each time the triggered ability of Rings of Brighthearth resolves.
If the ability has 
in its cost, the copy uses the same value of X.
The triggered ability of Rings of Brighthearth and the copy it creates both resolve before the ability that caused it to trigger. They resolve even if that ability is countered.
The copy will have the same targets as the ability it’s copying unless you choose new ones. You may change any number of the targets, including all of them or none of them. If, for one of the targets, you can’t choose a new legal target, then it remains unchanged (even if the current target is illegal).
If paying the activation cost of the ability includes sacrificing Rings of Brighthearth, the ability won’t be copied. At the time the ability is considered activated (after all costs are paid), Rings of Brighthearth is no longer on the battlefield.