msem-instigator

Spirited (When this enters, you may activate one of its activated abilities without paying its cost.)
{5}, {T}, Discard a card: Create a 0/0 colorless Construct artifact creature token with “This creature gets +1/+1 for each artifact you control.” It can't block this turn.

This spell costs {1} less to cast for each Scarecrow you control.
Other creatures you control get +0/+2 and have vigilance.

Whenever Uncanny Allocator enters or attacks, give any number of permanents and/or players with counters on them another counter of each kind already there.

Uncharted Haven enters tapped.
As Uncharted Haven enters, choose a color.
{T}: Add one mana of the chosen color.

When Uncovered Idol enters, scry 1.
{1}, Sacrifice Uncovered Idol: Put a +1/+1 counter on target creature. Activate only as a sorcery.

{T}: Add {C}.
{1}{R}, {T}, Discard a card: Exile the top card of your library. You may play it until the end of your next turn.
At the beginning of combat on your turn, if there are eight or more nonland cards in your graveyard, you may pay {2}{R}{R} and exile this land. When you do, it deals 5 damage to any target.

{T}: Add one mana of any color.
{T}, Sacrifice Unicorn of the Vale: Add three mana of any one color.

When Unity Spheres enters, create two 1/1 colorless Construct artifact creature tokens.
Tap two untapped creatures you control: Add two mana of any one color.

University Archive enters tapped.
When University Archive enters, look at the top card of your library. You may put it into your graveyard.
{T}: Add {U} or {R}.

{T}: Add {C}.
{1}, {T}: Add one mana of any color.

{T}, Pay 1 life: Add {U} or {B}.
{1}, {T}, Sacrifice Unlit Alley: Investigate. (Create a colorless Clue artifact token with “{2}, Sacrifice this artifact: Draw a card.”)

When Unmarked Vials enters, create a Vial token. (It's an artifact with “{1}, Sacrifice this and another permanent: Draw a card. Activate only during your turn.”)
{1}, {T}: Add one mana of any color.

Add X mana in any combination of colors, where X is the amount of mana spent to cast Unravel Shattered Worlds.
Coalesce {7} (You may cast this from your graveyard for {7}. If you do, it enters as a Horror creature after it resolves. Exile it if it would leave the battlefield or not resolve.)

Trample (This creature can deal excess combat damage to the player or planeswalker it's attacking.)
Unstable Borer attacks each combat if able.

Vanishing 2 (This permanent enters with two time counters on it. At the beginning of your upkeep, remove a time counter from it. When the last is removed, sacrifice it.)
{T}: Add {C}.
When Unstable Footing is put into your graveyard from the battlefield, if it had no time counters on it, search your library for a basic land card, put it onto the battlefield, then shuffle.

When Unstable Orb enters, draw a card.
{3}, {T}, Sacrifice Unstable Orb: It deals 2 damage to target creature.

{T}: Add {C}.
{T}, Sacrifice Untethered Spire: Choose target land card in your graveyard that was put there from the battlefield this turn. Return that card to your hand.

Untrekked Territory enters tapped.
{T}: Add {B} or {G}.
When Untrekked Territory enters, you may put a loyalty counter on a planeswalker you control.

Unzari Ruins enters tapped.
{T}: Add {C}.
Tap five untapped creatures you control: Unzari Ruins becomes a 10/10 Construct artifact creature with trample until end of turn. It's still a land.

({T}: Add {B} or {R}.)
Urban Wastelands enters tapped.
Cycling {2} ({2}, Discard this card: Draw a card.)

When Urn of Heroes enters, you may search your library for a legendary card, put that card into your graveyard, then shuffle.
{T}: Add {C}.

({T}: Add {B} or {R}.)
As Vacated Bar enters, you may pay {1}. If you don't, Vacated Bar enters tapped.

When Vale Ruins enters, you gain 1 life.
{T}, Sacrifice Vale Ruins: Search your library for a basic land card, put it onto the battlefield tapped, then shuffle.

Valley Falls enters tapped unless you control two or more white and/or blue permanents.
{T}: Add {W} or {U}.

As Vanquisher's Banner enters, choose a creature type.
Creatures you control of the chosen type get +1/+1.
Whenever you cast a creature spell of the chosen type, draw a card.