Alphael Brace of the Haligtree

Elphael Brace of the Haligtree enters the battlefield tapped.
{t}: Add {w}.
{w}, {t}: tap all untapped white creatures,
you gain 1 life for each creature tapped this way.
Activate only as a sorcery.
Whenever Elphael Brace of the Haligtree leaves
the battlefield, you take X damage, where X is
the number of lands you control.