Three Steps Ahead

Spree (Choose one or more additional costs.)
+ {1}{U} — Counter target spell.
+ {3} — Create a token that's a copy of target artifact or creature you control.
+ {2} — Draw two cards, then discard a card.

Island

Helm of the Host

At the beginning of combat on your turn, create a token that's a copy of equipped creature, except the token isn't legendary. That token gains haste.
Equip {5}

Irenicus's Vile Duplication

Create a token that's a copy of target creature you control, except the token has flying and it isn't legendary.

Second Harvest

For each token you control, create a token that's a copy of that permanent.

Glasspool Shore

Glasspool Shore enters tapped.
{T}: Add {U}.

Glasspool Mimic

You may have Glasspool Mimic enter as a copy of a creature you control, except it's a Shapeshifter Rogue in addition to its other types.

Glasspool Mimic // Glasspool Shore

Mirror Image

You may have Mirror Image enter as a copy of a creature you control.

Orvar, the All-Form

Changeling
Whenever you cast an instant or sorcery spell, if it targets one or more other permanents you control, create a token that's a copy of one of those permanents.
When a spell or ability an opponent controls causes you to discard this card, create a token that's a copy of target permanent.

Oltec Matterweaver

Whenever you cast a creature spell, choose one —
• Create a 1/1 colorless Gnome artifact creature token.
• Create a token that's a copy of target artifact token you control.

Wingmantle Chaplain

Defender
When Wingmantle Chaplain enters, create a 1/1 white Bird creature token with flying for each creature with defender you control.
Whenever another creature you control with defender enters, create a 1/1 white Bird creature token with flying.

Quasiduplicate

Create a token that's a copy of target creature you control.
Jump-start (You may cast this card from your graveyard by discarding a card in addition to paying its other costs. Then exile this card.)

Three Blind Mice

(As this Saga enters and after your draw step, add a lore counter. Sacrifice after IV.)
I — Create a 1/1 white Mouse creature token.
II, III — Create a token that's a copy of target token you control.
IV — Creatures you control get +1/+1 and gain vigilance until end of turn.

Esoteric Duplicator

Whenever you sacrifice Esoteric Duplicator or another artifact, you may pay {2}. If you do, at the beginning of the next end step, create a token that's a copy of that artifact.
{2}, Sacrifice Esoteric Duplicator: Draw a card.

Castle Vantress

Castle Vantress enters tapped unless you control an Island.
{T}: Add {U}.
{2}{U}{U}, {T}: Scry 2.

Phyrexian Metamorph

({U/P} can be paid with either {U} or 2 life.)
You may have Phyrexian Metamorph enter as a copy of any artifact or creature on the battlefield, except it's an artifact in addition to its other types.

Worldwalker Helm

If you would create one or more artifact tokens, instead create those tokens plus an additional Map token. (It's an artifact with "{1}, {T}, Sacrifice this artifact: Target creature you control explores. Activate only as a sorcery.")
{1}{U}, {T}: Create a token that's a copy of target artifact token you control.

Simulacrum Synthesizer

When Simulacrum Synthesizer enters, scry 2.
Whenever another artifact you control with mana value 3 or greater enters, create a 0/0 colorless Construct artifact creature token with "This creature gets +1/+1 for each artifact you control."

Vesuvan Duplimancy

Whenever you cast a spell that targets only a single artifact or creature you control, create a token that's a copy of that artifact or creature, except it's not legendary.

Temple of Enlightenment

Temple of Enlightenment enters tapped.
When Temple of Enlightenment enters, scry 1.
{T}: Add {W} or {U}.

Thalia's Lieutenant

When Thalia's Lieutenant enters, put a +1/+1 counter on each other Human you control.
Whenever another Human you control enters, put a +1/+1 counter on Thalia's Lieutenant.

Ghastly Mimicry

Enchant creature
At the beginning of your upkeep, create a token that's a copy of enchanted creature, except it's a Spirit in addition to its other types.
If Ghastly Mimicry would be put into a graveyard from anywhere, exile it instead.

Mirrorhall Mimic

You may have Mirrorhall Mimic enter as a copy of any creature on the battlefield, except it's a Spirit in addition to its other types.
Disturb {3}{U}{U} (You may cast this card from your graveyard transformed for its disturb cost.)

Mirrorhall Mimic // Ghastly Mimicry

Cackling Counterpart

Create a token that's a copy of target creature you control.
Flashback {5}{U}{U} (You may cast this card from your graveyard for its flashback cost. Then exile it.)

Plains

Meticulous Archive

({T}: Add {W} or {U}.)
Meticulous Archive enters tapped.
When Meticulous Archive enters, surveil 1. (Look at the top card of your library. You may put it into your graveyard.)