Master Emerald

Protection from everything.
You may choose not to untap Master Emerald
during your untap step.
{x}, {t}, Tap seven other Emeralds: X target
nontoken creatures get +10/+10 and gain Flying,
Trample, and protection from everything for as
long as Master Emerald remains tapped.
At the end of your turn, if Master Emerald is
tapped, sacrifice a Ring token. If you cannot,
sacrifice all Emeralds you control.