Mental Misstep

({U/P} can be paid with either {U} or 2 life.)
Counter target spell with mana value 1.

Simian Spirit Guide

Exile Simian Spirit Guide from your hand: Add {R}.

Underworld Breach

Each nonland card in your graveyard has escape. The escape cost is equal to the card's mana cost plus exile three other cards from your graveyard. (You may cast cards from your graveyard for their escape cost.)
At the beginning of the end step, sacrifice Underworld Breach.

Ranger-Captain of Eos

When Ranger-Captain of Eos enters, you may search your library for a creature card with mana value 1 or less, reveal it, put it into your hand, then shuffle.
Sacrifice Ranger-Captain of Eos: Your opponents can't cast noncreature spells this turn.

Derevi, Empyrial Tactician

Flying
When Derevi, Empyrial Tactician enters and whenever a creature you control deals combat damage to a player, you may tap or untap target permanent.
{1}{G}{W}{U}: Put Derevi onto the battlefield from the command zone.

Flusterstorm

Counter target instant or sorcery spell unless its controller pays {1}.
Storm (When you cast this spell, copy it for each spell cast before it this turn. You may choose new targets for the copies.)

Arcane Signet

{T}: Add one mana of any color in your commander's color identity.

Culling Ritual

Destroy each nonland permanent with mana value 2 or less. Add {B} or {G} for each permanent destroyed this way.

Fierce Guardianship

If you control a commander, you may cast this spell without paying its mana cost.
Counter target noncreature spell.

Rhystic Study

Whenever an opponent casts a spell, you may draw a card unless that player pays {1}.

Gamble

Search your library for a card, put that card into your hand, discard a card at random, then shuffle.

Elvish Spirit Guide

Exile Elvish Spirit Guide from your hand: Add {G}.

Noble Hierarch

Exalted (Whenever a creature you control attacks alone, that creature gets +1/+1 until end of turn.)
{T}: Add {G}, {W}, or {U}.

Intuition

Search your library for three cards and reveal them. Target opponent chooses one. Put that card into your hand and the rest into your graveyard. Then shuffle.

Force of Will

You may pay 1 life and exile a blue card from your hand rather than pay this spell's mana cost.
Counter target spell.

Deflecting Swat

If you control a commander, you may cast this spell without paying its mana cost.
You may choose new targets for target spell or ability.

Chrome Mox

Imprint — When Chrome Mox enters, you may exile a nonartifact, nonland card from your hand.
{T}: Add one mana of any of the exiled card's colors.

Esper Sentinel

Whenever an opponent casts their first noncreature spell each turn, draw a card unless that player pays {X}, where X is Esper Sentinel's power.

Worldly Tutor

Search your library for a creature card, reveal it, then shuffle and put the card on top.

Sol Ring

Final Fortune

Take an extra turn after this one. At the beginning of that turn's end step, you lose the game.

Deathrite Shaman

{T}: Exile target land card from a graveyard. Add one mana of any color.
{B}, {T}: Exile target instant or sorcery card from a graveyard. Each opponent loses 2 life.
{G}, {T}: Exile target creature card from a graveyard. You gain 2 life.

Diabolic Intent

As an additional cost to cast this spell, sacrifice a creature.
Search your library for a card, put that card into your hand, then shuffle.

Thassa's Oracle

When Thassa's Oracle enters, look at the top X cards of your library, where X is your devotion to blue. Put up to one of them on top of your library and the rest on the bottom of your library in a random order. If X is greater than or equal to the number of cards in your library, you win the game. (Each {U} in the mana costs of permanents you control counts toward your devotion to blue.)

Birds of Paradise

Vampiric Tutor

Search your library for a card, then shuffle and put that card on top. You lose 2 life.

Dockside Extortionist

When Dockside Extortionist enters, create X Treasure tokens, where X is the number of artifacts and enchantments your opponents control. (Treasure tokens are artifacts with "{T}, Sacrifice this artifact: Add one mana of any color.")

Gitaxian Probe

({U/P} can be paid with either {U} or 2 life.)
Look at target player's hand.
Draw a card.

Silence

Your opponents can't cast spells this turn.

Najeela, the Blade-Blossom

Whenever a Warrior attacks, you may have its controller create a 1/1 white Warrior creature token that's tapped and attacking.
{W}{U}{B}{R}{G}: Untap all attacking creatures. They gain trample, lifelink, and haste until end of turn. After this phase, there is an additional combat phase. Activate only during combat.

Ad Nauseam

Reveal the top card of your library and put that card into your hand. You lose life equal to its mana value. You may repeat this process any number of times.