Yue, the Moon Spirit

You can tap any untapped creature or artifact you control to pay a waterbend cost, even one you haven't controlled continuously since the beginning of your most recent turn.

If you cast a card "without paying its mana cost," you can't choose to cast it for any alternative costs. You can, however, pay additional costs. If the card has any mandatory additional costs, such as that of Cathartic Reunion, you must pay those to cast the card.

Even if the cost of the spell or ability that waterbend is part of increases or decreases, you still may only tap artifacts or creatures to pay for costs up to the amount of the generic mana in the waterbend cost.