Soulbond Mechanic

Soulbond (You may pair this creature with another unpaired creature when either enters the battlefield. They remain paired for as long as you control both of them.)
Basically costs 50% more than it would if you were adding the same mechanic, without soulbond. So an evergreen mechanic added with soulbond costs about .5 mana, rather than {0} to add to a 1/1. Situational abilities (protection from zombies) cost about {0}.