Rikala, Homarid King [Mystery Booster: Commander Edition]

At the beginning of your upkeep, put a tide counter on Rikala. Then if there are four or more tide counters on Rikala, remove them.
Creatures you control get +1/+0 for each tide counter on Rikala.
Whenever you tap an Island for mana, if there are three or more tide counters on Rikala, add an additional U.