The Darksign

Shroud, indestructible, devoid.
X is half of the target creature's converted mana
cost, rounded up. You may not target a creature
with the subtype Boss, or any tokens.
Enchanted creature gets darksign 1 (stackable).
This enchantment is permanantly attached to the
enchanted creature until the end of the game,
regardless of if the creature is killed, destroyed,
exiled, or changed into something else.