Lullmage's Domination
Sorcery
This spell costs 
less to cast if it targets a creature whose controller has eight or more cards in their graveyard.
Gain control of target creature with converted mana cost X.
"One spell to quiet the Roil, one to quash the will. The principle is the same."
Illustrated by
Zendikar Rising#66UncommonEnglishLegality
Rulings
An ability that offers a bonus if an opponent has eight or more cards in their graveyard won’t provide additional benefits if more than one opponent has eight or more cards in their graveyard. There are also no additional benefits no matter how many cards are in an opponent’s graveyard, as long as there are at least eight.
In a multiplayer game, once an opponent leaves the game, they won’t be considered for such an effect, no matter how many cards they had in their graveyard before leaving the game.