msem-instigator

Vision (Whenever this or another creature enters the battlefield under your control, reveal the top card of your library. Then you may put that card into your graveyard.)
Whenever Ulek Windrider envisions an instant or sorcery card, it gets +1/+0 and gains flying until end of turn.

Encourage ({T}: Another target creature you control gets +1/+1 until end of turn. Encourage only as a sorcery.)
Whenever a creature deals combat damage to a player, if it was encouraged by Unbeholden Navigator this turn, draw a card.

Unbound Spirit can't be blocked.
When you attain Unbound Spirit, tap target creature. That creature doesn't untap during its controller's next untap step.

Spend only mana produced by Treasures to cast spells.
{2}, Discard a card: Create two Treasure tokens.

Unceasing Flames deals X damage to any target, where X is 2 plus the number of cards named Unceasing Flames in your graveyard.
Conjure three cards named Unceasing Flames and shuffle them into your main library.

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

Target creature can't be blocked this turn.
Compose (Then if you cast this from your hand, exile it and create a Saga token with “III—You may cast a copy of this card from exile without paying its mana cost.”)

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

Enchant creature
Enchanted creature gets +1/+0 and has menace. (That creature can't be blocked except by two or more creatures.)

{T}, Pay 1 life: Add one mana of any color that a land an opponent controls could produce.

Colossal 2—{4}{B} (You may cast this for its colossal cost to have it enter with two +1/+1 counters; or pay {4}{B} as a sorcery: Put two +1/+1 counters on it if it has none.)
Lifelink

Enchant creature
Enchanted creature has first strike. (That creature deals combat damage before creatures without first strike.)

Return target creature card with mana value 3 or less from your graveyard to the battlefield.
Cycling {2} ({2}, Discard this card: Draw a card.)

Unending Slime enters the battlefield with X +1/+1 counters on it.
{2}{G}{G}{G}: Return Unending Slime from your graveyard to your hand.

Enchant land
When Unexplored Regions enters the battlefield, draw a card.
Enchanted land is an artifact in addition to its other types and has “{T}: Add one mana of any color.”

Flying, vigilance
When you attain Unfallen Angel, target opponent discards a card.

Unfettered Noble can't be blocked unless defending player pays 3 life, discards a card, or sacrifices a nonland permanent for each creature they control that's blocking it.
Sacrifice a nonland permanent: Unfettered Noble gains indestructible until end of turn.

Return target creature card from your graveyard to your hand.
Inscribe {3}{B} ({3}{B}: Exile this card from your hand inscribed on a creature you control. Whenever that creature attacks, its controller may cast a copy of the inscribed card without paying its mana cost. Inscribe only as a sorcery.)

Target creature can't block until end of turn. If that creature had a Steed attached to it, unattach that Steed and it can't block until end of turn.
Draw a card.

Other creatures you control get +1/+0.
At the beginning of combat on your turn, create a 1/1 red Human creature token with haste.

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

Target player loses 3 life.

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

Conjure six duplicates of target instant or sorcery card in a graveyard into your main library. Then shuffle.
Draw a card.

{G/W}: If Unlikeliest Heroes doesn't have a +1/+1 counter on it, put a +1/+1 counter on it.
{2}{G/W}{G/W}: If Unlikeliest Heroes has a +1/+1 counter on it and doesn't have vigilance, put two +1/+1 counters and a vigilance counter on it.
{3}{G/W}{G/W}{G/W}: If Unlikeliest Heroes has vigilance and not indestructible, put four +1/+1 counters and an indestructible counter on it.