Nadir Kraken

Whenever you draw a card, you may pay {1}. If you do, put a +1/+1 counter on Nadir Kraken and create a 1/1 blue Tentacle creature token.

Wavebreak Hippocamp

Whenever you cast your first spell during each opponent's turn, draw a card.

Temple of Enlightenment

Temple of Enlightenment enters the battlefield tapped.
When Temple of Enlightenment enters the battlefield, scry 1.
{T}: Add {W} or {U}.

Exotic Pets

Create two 1/1 blue Fish creature tokens with "This creature can't be blocked." Then for each kind of counter among creatures you control, put a counter of that kind on either of those tokens.

Riptide Turtle

Kill Shot

Slip Out the Back

Put a +1/+1 counter on target creature. It phases out. (Treat it and anything attached to it as though they don't exist until its controller's next turn.)

Staggering Insight

Enchant creature
Enchanted creature gets +1/+1 and has lifelink and "Whenever this creature deals combat damage to a player, draw a card."

Stinging Lionfish

Whenever you cast your first spell during each opponent's turn, you may tap or untap target nonland permanent.

Refuse to Yield

Target creature gets +2/+7 until end of turn. Untap it.

Plains

Knockout Blow

This spell costs {2} less to cast if it targets a red creature.
Knockout Blow deals 4 damage to target attacking or blocking creature and you gain 2 life.

Island

Reservoir Kraken

Trample, ward {2}
At the beginning of each combat, if Reservoir Kraken is untapped, any opponent may tap an untapped creature they control. If they do, tap Reservoir Kraken and create a 1/1 blue Fish creature token with "This creature can't be blocked."