Kopala, Warden of Waves

Mana cost: {1}{U}{U}
Type: Legendary Creature — Merfolk Wizard
Power / toughness: 2 / 2
Set: Ixalan Promos #61s (rare)

Spells your opponents cast that target a Merfolk you control cost {2} more to cast.
Abilities your opponents activate that target a Merfolk you control cost {2} more to activate.

Kopala, Warden of Waves has 4 printings, first in Ixalan (2017). EDHREC ranks it #4,223 among Commander cards. It appears most in Hakbal of the Surging Soul decks (22,777 on EDHREC). 1 public deck on TCG runs it. It has 4 official rulings.

Legality

commander: legal
legacy: legal
vintage: legal
pauper: not legal
modern: legal
pioneer: legal
standard: not legal
brawl: legal

Public decks that run Kopala, Warden of Waves

Explorers of the Deep - The Lost Caverns of Ixalan Commander, led by Hakbal of the Surging Soul

Commanders that run Kopala, Warden of Waves most

Deck counts from EDHREC.

Hakbal of the Surging Soul: 22,777 decks
Kumena, Tyrant of Orazca: 4,392 decks
Namor the Sub-Mariner: 2,823 decks
Svyelun of Sea and Sky: 1,450 decks
Sygg, Wanderwine Wisdom // Sygg, Wanderbrine Shield: 1,413 decks
Emperor Mihail II: 877 decks
Sygg, River Guide: 568 decks
Nicanzil, Current Conductor: 537 decks

Often played with Kopala, Warden of Waves

Cards that show up in the same decks on EDHREC.

Rulings

2017-09-29: Activated abilities contain a colon. They're generally written "[Cost]: [Effect]."
2017-09-29: Spells and abilities that target more than one Merfolk you control cost only {2} more to cast or activate.
2017-09-29: 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.
2017-09-29: Kopala's abilities won't affect triggered abilities (starting with "when," "whenever," or "at") that target a Merfolk you control.