Have

Kitsune's Technique

Sneak {1}{U} (You may cast this spell for {1}{U} if you also return an unblocked attacker you control to hand during the declare blockers step.)
Target opponent mills half their library, rounded up.

Getting

Frog Butler

Deathtouch
{T}: Add one mana of any color.
{2}: This creature gains reach until end of turn.

Build Box

Mikey & Leo, Chaos & Order

Whenever you put a counter on a creature you control, draw a card. This ability triggers only once each turn.

Don & Leo, Problem Solvers

Vigilance
At the beginning of your end step, exile up to one target artifact you control and up to one target creature you control. Then return them to the battlefield under their owners' control.

Michelangelo, Improviser

Sneak {2}{G}{G} (You may cast this spell for {2}{G}{G} if you also return an unblocked attacker you control to hand during the declare blockers step. He enters tapped and attacking.)
Whenever Michelangelo deals combat damage to a player, you may put a creature card and/or a land card from your hand onto the battlefield.

Raph & Mikey, Troublemakers

Trample, haste
Whenever Raph & Mikey attack, reveal cards from the top of your library until you reveal a creature card. Put that card onto the battlefield tapped and attacking and the rest on the bottom of your library in a random order.

Weather Maker

Landfall — Whenever a land you control enters, put a charge counter on this artifact.
{T}: Add one mana of any color.
{T}, Remove two charge counters from this artifact: Add {C}{C}.
{T}, Remove three charge counters from this artifact: It deals 3 damage to any target.

Savanti Romero, Time's Exile

Trample
At the beginning of combat on your turn, put a +1/+1 counter on Savanti Romero. Then you draw X cards and lose X life, where X is the number of counters on Savanti Romero.

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.

Leonardo, Sewer Samurai

Sneak {2}{W}{W}
Double strike
During your turn, you may cast creature spells with power or toughness 1 or less from your graveyard. If you cast a spell this way, that creature enters with a finality counter on it. (If a creature with a finality counter on it would die, exile it instead.)

Raph & Leo, Sibling Rivals

Whenever Raph & Leo attack, if it's the first combat phase of the turn, untap one or two target attacking creatures. After this phase, there is an additional combat phase.

Retro-Mutation

Flash
Enchant creature
Enchanted creature is a Turtle with base power and toughness 0/1. It can't attack and loses all abilities. (It also loses all other creature types.)

Saved by the Shell

This spell costs {1} less to cast if you control a Turtle.
Put a +1/+1 counter on target creature you control. It gains trample, hexproof, and indestructible until end of turn.

Dimensional Exile

Enchant basic land you control
When this Aura enters, exile target creature an opponent controls until this Aura leaves the battlefield.

Baxter, Fly in the Ointment

Whenever Baxter enters or attacks, each creature you control with a counter on it gains flying until end of turn.
Whenever you draw a card, put a +1/+1 counter on Baxter.

Venus, Torn Between Worlds

Whenever Venus is dealt damage, put that many +1/+1 counters on her. (She must survive the damage to get the counters.)
Whenever a creature you control with a counter on it deals combat damage to a player, you may pay {U}. If you do, draw a card.

Transdimensional Bovine

Flying
{T}: Add two mana of any one color.

Mikey & Don, Party Planners

Ward {2}
You may look at the top card of your library any time.
You may play lands and cast Mutant, Ninja, or Turtle spells from the top of your library. If you cast a creature spell this way, that creature enters with an additional +1/+1 counter on it.

Raphael, Tough Turtle

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

Michelangelo, Weirdness to 11

When Michelangelo 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.")
If one or more +1/+1 counters would be put on a creature you control, that many plus one +1/+1 counters are put on it instead.

Shredder's Armor

Equipped creature gets +2/+1.
When this Equipment enters, attach it to target creature you control.
Equip—Sacrifice another nonland permanent. Activate only once each turn.

Michelangelo, Mutant BFF

Each creature you control with a counter on it can't be blocked by more than one creature.
Whenever Michelangelo enters or attacks, 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.")

Donatello, Gadget Master

Sneak {1}{U} (You may cast this spell for {1}{U} if you also return an unblocked attacker you control to hand during the declare blockers step. He enters tapped and attacking.)
Whenever Donatello deals combat damage to a player, create a token that's a copy of target artifact you control.

Leatherhead, Swamp Stalker

Trample
Leatherhead enters with a hexproof counter on her.
Whenever Leatherhead deals combat damage to a player, you may remove a counter from her. When you do, destroy target artifact or enchantment that player controls.

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.)

Improvised Arsenal

Equipped creature gets +1/+0 for each artifact you control.
{4}{R}: Create a token that's a copy of this Equipment.
Equip {R}

Bespoke Bō

When this Equipment enters, return up to one other target nonland permanent to its owner's hand.
Equipped creature gets +2/+1 and has vigilance.
Equip {3} ({3}: Attach to target creature you control. Equip only as a sorcery.)

Level Up

Enchant creature
When this Aura enters, put a +1/+1 counter on enchanted creature.
Enchanted creature has "Whenever this creature attacks, double the number of +1/+1 counters on it. Then if it has power 10 or greater, draw a card."

Groundchuck & Dirtbag

Trample
Whenever you tap a land for mana, add {G}.

Triceraton Commander

Flying
Whenever this creature attacks, Dinosaurs you control other than this creature get +1/+1 and gain flying until end of turn.
When this creature enters, create X 2/2 white Dinosaur Soldier creature tokens.

Donatello, Way with Machines

Flying
Whenever an artifact you control enters, put a +1/+1 counter on Donatello.

High Score

If one or more +1/+1 counters would be put on a creature you control, that many plus one +1/+1 counters are put on it instead.
At the beginning of your end step, draw a card if you control a creature with the greatest power among creatures on the battlefield.

Conqueror's Flail

Equipped creature gets +1/+1 for each color among permanents you control.
As long as this Equipment is attached to a creature, your opponents can't cast spells during your turn.
Equip {2}

Donatello, Mutant Mechanic

{T}: Put three +1/+1 counters on target artifact you control. If it isn't a creature, it becomes a 0/0 Robot creature in addition to its other types. Activate only as a sorcery.
Whenever an artifact you control is put into a graveyard from the battlefield, if it had counters on it, put those counters on up to one target artifact or creature you control.

Quintessential Katana

Equipped creature gets +1/+1 and has "Whenever this creature deals combat damage, untap it and you gain 2 life."
Whenever a Ninja you control enters, you may attach this Equipment to it.
Equip {2} ({2}: Attach to target creature you control. Equip only as a sorcery.)

Tenderize

Target creature you control deals damage equal to its power to target creature an opponent controls.

Leonardo, Cutting Edge

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.)
Lifelink
Whenever you gain life, put a +1/+1 counter on Leonardo.