Aether Sentinel

Shroud, Indestructible
If a player would sacrifice or exile a permanent
as part of the cost of an activated ability, that permanent and Aether Sentinel phase out
instead and that activated ability is countered.
When Aether Sentinel phases in, it gets a -1/-1
counter.
Pay 2 life: Aether Sentinel phases out. Any
player may activate this ability.