Tempest Caller

When Tempest Caller enters, tap all creatures target opponent controls.

Incremental Growth

Put a +1/+1 counter on target creature, two +1/+1 counters on another target creature, and three +1/+1 counters on a third target creature.

Prey Upon

Target creature you control fights target creature you don't control. (Each deals damage equal to its power to the other.)

Deeproot Warrior

Whenever Deeproot Warrior becomes blocked, it gets +1/+1 until end of turn.

Kumena's Speaker

Kumena's Speaker gets +1/+1 as long as you control another Merfolk or an Island.

Waker of the Wilds

{X}{G}{G}: Put X +1/+1 counters on target land you control. That land becomes a 0/0 Elemental creature with haste. It's still a land.

Vineshaper Mystic

When Vineshaper Mystic enters, put a +1/+1 counter on each of up to two target Merfolk you control.

Soul of the Harvest

Trample
Whenever another nontoken creature you control enters, you may draw a card.

Air Elemental

Jungle Barrier

Defender (This creature can't attack.)
When Jungle Barrier enters, draw a card.

Fleetfeather Cockatrice

Flash (You may cast this spell any time you could cast an instant.)
Flying, deathtouch
{5}{G}{U}: Monstrosity 3. (If this creature isn't monstrous, put three +1/+1 counters on it and it becomes monstrous.)

Aether Gale

Return six target nonland permanents to their owners' hands.

Island

Rancor

Enchant creature
Enchanted creature gets +2/+0 and has trample.
When Rancor is put into a graveyard from the battlefield, return Rancor to its owner's hand.

Unsummon

Return target creature to its owner's hand.

Merfolk Sovereign

Other Merfolk creatures you control get +1/+1.
{T}: Target Merfolk creature can't be blocked this turn.

Drakewing Krasis

Shapers of Nature

{3}{G}: Put a +1/+1 counter on target creature.
{2}{U}, Remove a +1/+1 counter from a creature you control: Draw a card.

Giant Growth

Target creature gets +3/+3 until end of turn.

Vigean Hydropon

Graft 5 (This creature enters with five +1/+1 counters on it. Whenever another creature enters, you may move a +1/+1 counter from this creature onto it.)
Vigean Hydropon can't attack or block.