Game Over

This spell costs {2} less to cast if a player's life total is less than or equal to half their starting life total.
Destroy all creatures.

Splinter, the Mentor

Menace
Whenever Splinter or another nontoken creature you control leaves the battlefield, create a Mutagen token.
Partner—Character select (You can have two commanders if both have this ability.)

Bebop, Skull & Crossbones

Partner with Rocksteady, Mutant Marauder (When this creature enters, target player may put Rocksteady into their hand from their library, then shuffle.)
Deathtouch
Whenever Bebop deals combat damage to a player, you may draw X cards, where X is the number of counters on Bebop. If you do, you lose X life.

Paramecia Coloniex

When this creature enters, mill three cards. (Put the top three cards of your library into your graveyard.)
When this creature dies, you may exile it. When you do, put target creature card from your graveyard on top of your library.

Armaggon, Future Shark

Flash
When Armaggon enters, destroy up to three target creatures.

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.

Foot Chopper

When this Equipment enters, create a 1/1 black Ninja creature token, then attach this Equipment to it.
Equipped creature has flying.
Whenever equipped creature deals combat damage to a player, you may sacrifice it. If you do, draw cards equal to its power.
Equip {2}

Shark Shredder, Killer Clone

Sneak {3}{B}{B}
First strike
Whenever Shark Shredder deals combat damage to a player, put up to one target creature card from that player's graveyard onto the battlefield under your control. It enters tapped and attacking that player.

Anchovy & Banana Pizza

When this artifact enters, destroy target creature.
{2}, {T}, Sacrifice this artifact: You gain 3 life.

The Cloning of Shredder

(As this Saga enters and after your draw step, add a lore counter. Sacrifice after III.)
I — Exile target creature card from your graveyard. Create a token that's a copy of it, except it isn't legendary and is a Mutant in addition to its other types.
II, III — Create a token that's a copy of a card exiled with this Saga, except it isn't legendary and is a Mutant in addition to its other types.

Dimension X Pizzasaur

When this creature enters, put two +1/+1 counters on target creature. When you do, destroy up to one target creature with mana value less than or equal to the number of counters among permanents you control.
{2}, {T}, Sacrifice this creature: You gain 3 life and each opponent loses 3 life.

South Wind Avatar

Deathtouch
Whenever another creature you control dies, you gain life equal to its toughness.
Whenever you gain life, each opponent loses 1 life.

Swift Demise

Swift Demise deals 1 damage to target creature. Then destroy each creature you don't control that was dealt damage this turn.

Oroku Saki, Shredder Rising

Sneak {1}{B} (You may cast this spell for {1}{B} if you also return an unblocked attacker you control to hand during the declare blockers step. He enters tapped and attacking.)
Whenever Oroku Saki deals combat damage to a player, you draw a card and lose 1 life.

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.

Foot Mystic

Lifelink
Disappear — When this creature enters, if a permanent left the battlefield under your control this turn, create a 1/1 black Ninja creature token.

Bebop, Warthog Warrior

Menace (This creature can't be blocked except by two or more creatures.)
Rhinos you control have menace.
Swampcycling {2} ({2}, Discard this card: Search your library for a Swamp card, reveal it, put it into your hand, then shuffle.)

Super Shredder

Menace
Whenever another permanent leaves the battlefield, put a +1/+1 counter on Super Shredder.

Shredder, Shadow Master

Whenever Shredder attacks a player, for each other opponent, create a token that's a copy of Shredder tapped and attacking that player, except it isn't legendary. Sacrifice those tokens at end of combat.
Whenever Shredder deals combat damage to a player, that player loses half their life, rounded up.

Death in the Family

Exile target creature with mana value 3 or less.

Rat King, Pale Piper

Menace
Whenever Rat King or another nontoken creature you control leaves the battlefield, create a 1/1 black Rat creature token.
{2}, Sacrifice a token: Draw a card.

Shredder's Revenge

Choose one —
• Target player discards two cards.
• Target player draws two cards and loses 2 life.

Pain 101

Until end of turn, target creature gains deathtouch and "When this creature dies, return it to the battlefield tapped under its owner's control."

Dream Beavers

Flying
When this creature enters, each opponent loses 1 life and you gain 1 life. Scry 1. (Look at the top card of your library. You may put that card on the bottom.)

Swamp

Stomped by the Foot

Kicker—Sacrifice an artifact or creature. (You may sacrifice an artifact or creature in addition to any other costs as you cast this spell.)
Target creature gets -2/-2 until end of turn. If this spell was kicked, that creature gets -5/-5 until end of turn instead.

Insectoid Exterminator

Flying
Disappear — At the beginning of your end step, if a permanent left the battlefield under your control this turn, scry 1. (Look at the top card of your library. You may put that card on the bottom.)

Ninja Teen

(Gain the next level as a sorcery to add its ability.)
Whenever a creature you control leaves the battlefield, each opponent loses 1 life.
{1}{B}: Level 2
Creatures you control get +1/+0 and have menace.
{B}: Level 3
Creature cards in your graveyard have sneak {3}{B}.
You may cast creature spells from your graveyard using their sneak abilities.

Shredder's Technique

Sneak {B} (You may cast this spell for {B} if you also return an unblocked attacker you control to hand during the declare blockers step.)
Destroy target creature or enchantment. If an enchantment was destroyed this way, you lose 2 life.

Madame Null, Power Broker

Deathtouch
Whenever another creature you control enters, you may pay life equal to its power. If you do, put that many +1/+1 counters on it.

Splinter's Technique

Sneak {1}{B} (You may cast this spell for {1}{B} if you also return an unblocked attacker you control to hand during the declare blockers step.)
Search your library for a card, put that card into your hand, then shuffle.