April O'Neil, Kunoichi Trainee

When April O'Neil enters, scry 2. (Look at the top two cards of your library, then put any number of them on the bottom and the rest on top in any order.)
April O'Neil can't be blocked by creatures with power 3 or greater.

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.

Mouser Foundry

When this artifact enters or leaves the battlefield, create a 1/1 colorless Robot artifact creature token.
{4}{R}, Sacrifice this artifact: It deals 3 damage to target creature.

Hamato Guardian Stance

Target creature gets +1/+3 and gains flying until end of turn. Scry 1. (Look at the top card of your library. You may put that card on the bottom.)

Mountain

Return to the Sewers

Target creature's owner puts it on their choice of the top or bottom of their library. You 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.")

Expressive Firedancer

Opus — Whenever you cast an instant or sorcery spell, this creature gets +1/+1 until end of turn. If five or more mana was spent to cast that spell, this creature also gains double strike until end of turn.

Raphael, Tough Turtle

Alliance — Whenever another creature you control enters, Raphael deals 1 damage to target opponent.

Foot Headquarters

This land enters tapped.
When this land enters, you gain 1 life.
{T}: Add {W} or {B}.

Terramorphic Expanse

{T}, Sacrifice this land: Search your library for a basic land card, put it onto the battlefield tapped, then shuffle.

Island

Sewer-veillance Cam

Flash
When this artifact enters or leaves the battlefield, you may tap or untap target creature.
{3}{U}, Sacrifice this artifact: Draw two cards.

TCRI Building

This land enters tapped.
When this land enters, you gain 1 life.
{T}: Add {U} or {R}.

Donatello, Turtle Techie

When Donatello enters, if you control an artifact, draw a card.

Thrill of Possibility

As an additional cost to cast this spell, discard a card.
Draw two cards.

Sundown Pass

This land enters tapped unless you control two or more other lands.
{T}: Add {R} or {W}.

Mutant Town Musicians

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

Nobody

When this creature enters, return up to one other target artifact you control to its owner's hand. Scry 1. (Look at the top card of your library. You may put that card on the bottom.)

Dimension X

This land enters tapped.
When this land enters, you gain 1 life.
{T}: Add {R} or {W}.

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.")

Plains

Hard-Won Jitte

Equipped creature has double strike.
Equip {2} ({2}: Attach to target creature you control. Equip only as a sorcery.)