Saw in Half

Destroy target creature. If that creature dies this way, its controller creates two tokens that are copies of that creature, except their power is half that creature's power and their toughness is half that creature's toughness. Round up each time.

Tamiyo Meets the Story Circle

(As this Saga enters and after your draw step, add a lore counter. Sacrifice after III.)
I — Until your next turn, whenever a creature attacks you or a planeswalker you control, it gets -2/-0 until end of turn.
II — Discard any number of cards, then investigate twice for each card discarded this way.
III — Shuffle up to three target cards from your graveyard into your library.

Theoretical Duplication

Whenever a nontoken creature an opponent controls enters this turn, create a token that's a copy of that creature.

Tamiyo, Compleated Sage

Compleated ({G/U/P} can be paid with {G}, {U}, or 2 life. If life was paid, this planeswalker enters with two fewer loyalty counters.)
+1: Tap up to one target artifact or creature. It doesn't untap during its controller's next untap step.
−X: Exile target nonland permanent card with mana value X from your graveyard. Create a token that's a copy of that card.
−7: Create Tamiyo's Notebook, a legendary colorless artifact token with "Spells you cast cost {2} less to cast" and "{T}: Draw a card."

Ashiok, Wicked Manipulator

If you would pay life while your library has at least that many cards in it, exile that many cards from the top of your library instead.
+1: Look at the top two cards of your library. Exile one of them and put the other into your hand.
−2: Create two 1/1 black Nightmare creature tokens with "At the beginning of combat on your turn, if a card was put into exile this turn, put a +1/+1 counter on this creature."
−7: Target player exiles the top X cards of their library, where X is the total mana value of cards you own in exile.

Uro, Titan of Nature's Wrath

When Uro enters, sacrifice it unless it escaped.
Whenever Uro enters or attacks, you gain 3 life and draw a card, then you may put a land card from your hand onto the battlefield.
Escape—{G}{G}{U}{U}, Exile five other cards from your graveyard. (You may cast this card from your graveyard for its escape cost.)

Desecrated Tomb

Whenever one or more creature cards leave your graveyard, create a 1/1 black Bat creature token with flying.

Nashi, Moon's Legacy

Menace, ward {1}
Whenever Nashi, Moon's Legacy attacks, exile up to one target legendary or Rat card from your graveyard and copy it. You may cast the copy. (You still pay its costs. A copy of a permanent spell becomes a token.)

Mirror Gallery

Ashiok, Dream Render

Spells and abilities your opponents control can't cause their controller to search their library.
−1: Target player mills four cards. Then exile each opponent's graveyard.

Tormod, the Desecrator

Whenever one or more cards leave your graveyard, create a tapped 2/2 black Zombie creature token.
Partner (You can have two commanders if both have partner.)

Animate Dead

Enchant creature card in a graveyard
When Animate Dead enters, if it's on the battlefield, it loses "enchant creature card in a graveyard" and gains "enchant creature put onto the battlefield with Animate Dead." Return enchanted creature card to the battlefield under your control and attach Animate Dead to it. When Animate Dead leaves the battlefield, that creature's controller sacrifices it.
Enchanted creature gets -1/-0.

Doppelgang

For each of X target permanents, create X tokens that are copies of that permanent.

The Wise Mothman

Flying
Whenever The Wise Mothman enters or attacks, each player gets a rad counter.
Whenever one or more nonland cards are milled, put a +1/+1 counter on each of up to X target creatures, where X is the number of nonland cards milled this way.

Stitcher's Supplier

When Stitcher's Supplier enters or dies, mill three cards. (Put the top three cards of your library into your graveyard.)

Sakashima of a Thousand Faces

You may have Sakashima of a Thousand Faces enter as a copy of another creature you control, except it has Sakashima of a Thousand Faces's other abilities.
The "legend rule" doesn't apply to permanents you control.
Partner (You can have two commanders if both have partner.)

Mirror Box

The "legend rule" doesn't apply to permanents you control.
Each legendary creature you control gets +1/+1.
Each nontoken creature you control gets +1/+1 for each other creature you control with the same name as that creature.