Put a tide counter on Tidal Influence when it is brought into play and during your upkeep. If there is one tide counter on Tidal Influence, all blue creatures get -2/-0. If there are three tide counters on Tidal Influence, all blue creatures get +2/+0. When there are four tide counters on Tidal Influence, remove them all. You may not cast Tidal Influence if there is another Tidal Influence in play.