Your life total is higher than or equal to an opponent's.
({1} magic symbol) available.
Steps
Activate Disciple of Griselbrand by paying ({1} magic symbol) and sacrificing Serra Avatar.
Serra Avatar triggers, shuffling itself into your library.
Resolve the Disciple of Griselbrand ability, causing you to gain life equal to Serra Avatar's toughness.
Sanguine Bond triggers, causing target opponent whose lifetotal is less than or equal to Serra Avatar's toughness to lose life equal to the life you gained.
The opponent loses the game due to having zero or less life.