Merfolk of the Depths

Flash (You may cast this spell any time you could cast an instant.)

Ivy Lane Denizen

Whenever another green creature you control enters, put a +1/+1 counter on target creature.

Shambleshark

Flash (You may cast this spell any time you could cast an instant.)
Evolve (Whenever a creature you control enters, if that creature has greater power or toughness than this creature, put a +1/+1 counter on this creature.)

Kraken Hatchling

Cloudfin Raptor

Flying
Evolve (Whenever a creature you control enters, if that creature has greater power or toughness than this creature, put a +1/+1 counter on this creature.)

Leyline Phantom

When Leyline Phantom deals combat damage, return it to its owner's hand. (Return it only if it survived combat.)

Elusive Krasis

Elusive Krasis can't be blocked.
Evolve (Whenever a creature you control enters, if that creature has greater power or toughness than this creature, put a +1/+1 counter on this creature.)

Crocanura

Reach (This creature can block creatures with flying.)
Evolve (Whenever a creature you control enters, if that creature has greater power or toughness than this creature, put a +1/+1 counter on this creature.)

Urban Evolution

Draw three cards. You may play an additional land this turn.

Bioshift

Move any number of +1/+1 counters from target creature onto another target creature with the same controller.

Chronomaton

{1}, {T}: Put a +1/+1 counter on Chronomaton.

Island

Hindervines

Prevent all combat damage that would be dealt this turn by creatures with no +1/+1 counters on them.

Unexpected Results

Shuffle your library, then reveal the top card. If it's a nonland card, you may cast it without paying its mana cost. If it's a land card, you may put it onto the battlefield and return Unexpected Results to its owner's hand.

Adaptive Snapjaw

Evolve (Whenever a creature you control enters, if that creature has greater power or toughness than this creature, put a +1/+1 counter on this creature.)

Frilled Oculus

{1}{G}: Frilled Oculus gets +2/+2 until end of turn. Activate only once each turn.

Crowned Ceratok

Trample
Each creature you control with a +1/+1 counter on it has trample.

Drakewing Krasis

Forced Adaptation

Enchant creature
At the beginning of your upkeep, put a +1/+1 counter on enchanted creature.

Forest

Sapphire Drake

Flying
Each creature you control with a +1/+1 counter on it has flying.

Sleep

Tap all creatures target player controls. Those creatures don't untap during that player's next untap step.

Zameck Guildmage

{G}{U}: This turn, each creature you control enters with an additional +1/+1 counter on it.
{G}{U}, Remove a +1/+1 counter from a creature you control: Draw a card.

Simic Keyrune

{T}: Add {G} or {U}.
{G}{U}: Simic Keyrune becomes a 2/3 green and blue Crab artifact creature with hexproof until end of turn. (It can't be the target of spells or abilities your opponents control.)

Encrust

Enchant artifact or creature
Enchanted permanent doesn't untap during its controller's untap step and its activated abilities can't be activated.

Fathom Mage

Evolve (Whenever a creature you control enters, if that creature has greater power or toughness than this creature, put a +1/+1 counter on this creature.)
Whenever a +1/+1 counter is put on Fathom Mage, you may draw a card.