Players won't know which player or planeswalker Reservoir Kraken will attack, if any, when deciding whether to tap an untapped creature for its triggered ability.

Each opponent in turn order may choose to tap an untapped creature as Reservoir Kraken's triggered ability resolves, even if a player earlier in the turn order already chose to tap a creature. Reservoir Kraken's controller will create a maximum of one Fish creature token each combat, no matter how many creatures were tapped.