The Cauldron of Eternity
Legendary Artifact
This spell costs 
less to cast for each creature card in your graveyard.
Whenever a creature you control dies, put it on the bottom of its owner's library.
, 
, Pay 2 life: Return target creature card from your graveyard to the battlefield. Activate only as a sorcery.
Tomasz Jedruszek
Throne of Eldraine (ELD)
• #352Rulings
To determine the total cost of a spell, start with the mana cost or alternative cost you're paying, add any cost increases, then apply any cost reductions. The mana value of the spell remains unchanged, no matter what the total cost to cast it was.
(wotc • 2019-10-04)
Once you announce that you're casting a spell, no player may take actions until the spell has been paid for. Notably, opponents can't try to change by how much a relic's cost is reduced.
(wotc • 2019-10-04)
The cost reduction ability reduces only the generic mana in the relic's cost. The colored mana must still be paid.
(wotc • 2019-10-04)
Rulings
To determine the total cost of a spell, start with the mana cost or alternative cost you're paying, add any cost increases, then apply any cost reductions. The mana value of the spell remains unchanged, no matter what the total cost to cast it was.
(wotc • 2019-10-04)
Once you announce that you're casting a spell, no player may take actions until the spell has been paid for. Notably, opponents can't try to change by how much a relic's cost is reduced.
(wotc • 2019-10-04)
The cost reduction ability reduces only the generic mana in the relic's cost. The colored mana must still be paid.
(wotc • 2019-10-04)