Tranquility Sliver

Slivers have Bestow {2}{x}, where {x} is the
creature spell cost. This Bestow can only target
creatures that share a color with it. (If Slivers
lose Bestow, resolve as Aura becoming unattached)
This creature can't attack or block.
Creatures enchanted by sliver cards can't attack
or block, and have the enchanting sliver's ability
in addition to their own.