Must attack each turn if possible.

At the beginning of your upkeep, put a +1/+1 counter on Primordial Ooze. At the end of your upkeep, pay X, where X is equal to the number of +1/+1 counters on Primordial Ooze, or Primordial Ooze deals X damage to you. If Primordial Ooze deals damage to you in this way, tap it.