Strengthening Apparition

Flying, Soulbond
Cumulative Upkeep {w}-(At the beginning of your upkeep, put an age counter on this creature, then sacrifice it unless you pay its cumulative upkeep cost for each age counter on it.)
As long as Strengthening Apperition is paired with another creature, each of those creatures gets +X/+X where X is the number of age counters on Strengthening Apperition.