Kopala, Warden of Waves

• WWizards of the Coast2017-09-29
  Official Ruling
  Activated abilities contain a colon. They're generally written "[Cost]: [Effect]."
• WWizards of the Coast2017-09-29
  Official Ruling
  Spells and abilities that target more than one Merfolk you control cost only more to cast or activate.
• WWizards of the Coast2017-09-29
  Official Ruling
  To determine the total cost of an opponent's spell that targets a Merfolk you control, start with the mana cost or alternative cost that player is paying, add any cost increases, then apply any cost reductions. The mana value of the spell remains unchanged, no matter what the total cost to cast it was.
• WWizards of the Coast2017-09-29
  Official Ruling
  Kopala's abilities won't affect triggered abilities (starting with "when," "whenever," or "at") that target a Merfolk you control.

Rulings via Scryfall