Tidal Influence

Cast this spell only if no permanents named Tidal Influence are on the battlefield. This enchantment enters with a tide counter on it. At the beginning of your upkeep, put a tide counter on this enchantment. As long as there is exactly one tide counter on this enchantment, all blue creatures get -2/-0. As long as there are exactly three tide counters on this enchantment, all blue creatures get +2/+0. Whenever there are four or more tide counters on this enchantment, remove all tide counters from it.