Okay so if my opponent use Spiral Pierce again, could I counter with Offering to Asha and/or Overrule? And with Overrule, the mana cost is 1 water, 1 light, and X. Is the X cost how ever many I want to use?
Yes, you can use either or those spells to try and counter Spell Pierce. And, you can choose whatever value you want for X, as long as you have the mana to pay for it.