Leonardo, Big Brother

Sneak {W} (You may cast this spell for {W} if you also return an unblocked attacker you control to hand during the declare blockers step. He enters tapped and attacking.)
Leonardo gets +1/+0 for each other creature you control.

Genku, Future Shaper

Whenever another nontoken permanent you control leaves the battlefield, choose one that hasn't been chosen this turn. Create a creature token with those characteristics.
• 2/2 white Fox with vigilance.
• 1/2 blue Moonfolk with flying.
• 1/1 black Rat with lifelink.
{3}{W}{U}: Put a +1/+1 counter on each creature you control.

Helpful Hunter

Leader's Talent

(Gain the next level as a sorcery to add its ability.)
Whenever you attack, put a +1/+1 counter on target attacking creature.
{2}{W}: Level 2
Whenever a creature you control leaves the battlefield, if it had a counter on it, you gain 2 life.
{3}{W}: Level 3
Whenever you cast a spell, put a +1/+1 counter on each creature you control.

Crustacean Commando

When this creature enters, create a Mutagen token. (It's an artifact with "{1}, {T}, Sacrifice this token: Put a +1/+1 counter on target creature. Activate only as a sorcery.")

Merrow Skyswimmer

Convoke (Your creatures can help cast this spell. Each creature you tap while casting this spell pays for {1} or one mana of that creature's color.)
Flying, vigilance
When this creature enters, create a 1/1 white and blue Merfolk creature token.

Utrom Scientists

When this creature enters, tap up to one target creature and put a stun counter on it. (If a permanent with a stun counter would become untapped, remove one from it instead.)

Stockman, Mad Fly-entist

Flying
When Stockman enters, draw a card, then discard a card.
Islandcycling {2} ({2}, Discard this card: Search your library for an Island card, reveal it, put it into your hand, then shuffle.)

Commander's Sphere

{T}: Add one mana of any color in your commander's color identity.
Sacrifice this artifact: Draw a card.

Crystal Shard

{3}, {T} or {U}, {T}: Return target creature to its owner's hand unless its controller pays {1}.

Aven Eternal

Flying
When this creature enters, amass Zombies 1. (Put a +1/+1 counter on an Army you control. It's also a Zombie. If you don't control an Army, create a 0/0 black Zombie Army creature token first.)

Leonardo, Leader in Blue

Sneak {3}{W}{W} (You may cast this spell for {3}{W}{W} if you also return an unblocked attacker you control to hand during the declare blockers step. He enters tapped and attacking.)
When Leonardo enters, if his sneak cost was paid, creatures you control get +2/+0 until end of turn.
{1}{W}: Leonardo gains first strike until end of turn.

East Wind Avatar

Flying, vigilance
Alliance — Whenever another creature you control enters, this creature gets +1/+0 until end of turn.

Mighty Mutanimals

When this creature enters, create a 2/2 red Mutant creature token.
Alliance — Whenever another creature you control enters, put a +1/+1 counter on target creature you control.

Sally Pride, Lioness Leader

When Sally Pride enters, create X 2/2 red Mutant creature tokens, where X is the number of nontoken creatures you control.
Whenever Sally Pride attacks, put a +1/+1 counter on each creature you control.

Hide on the Ceiling

Exile X target artifacts and/or creatures. Return the exiled cards to the battlefield under their owners' control at the beginning of the next end step.

City Pigeon

Flying
When this creature leaves the battlefield, create a Food token. (It's an artifact with "{2}, {T}, Sacrifice this token: You gain 3 life.")

Kitsune, Dragon's Daughter

Vigilance
Whenever Kitsune enters or deals combat damage to a player, you may exchange control of two other target creatures controlled by different players.

Selfless Police Captain

This creature enters with a +1/+1 counter on it.
When this creature leaves the battlefield, put its +1/+1 counters on target creature you control.

Spider-Man No More

Enchant creature
Enchanted creature is a Citizen with base power and toughness 1/1. It has defender and loses all other abilities. (It also loses all other creature types.)