Solemnity

Players can't get counters.
Counters can't be put on artifacts, creatures, enchantments, or lands.

Arcane Signet

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

Aven Mindcensor

Flash
Flying
If an opponent would search a library, that player searches the top four cards of that library instead.

Counterspell

Mystic Remora

Cumulative upkeep {1} (At the beginning of your upkeep, put an age counter on this permanent, then sacrifice it unless you pay its upkeep cost for each age counter on it.)
Whenever an opponent casts a noncreature spell, you may draw a card unless that player pays {4}.

Talisman of Progress

{T}: Add {C}.
{T}: Add {W} or {U}. This artifact deals 1 damage to you.

Archivist of Oghma

Flash
Whenever an opponent searches their library, you gain 1 life and draw a card.

Swords to Plowshares

Exile target creature. Its controller gains life equal to its power.

Grand Arbiter Augustin IV

White spells you cast cost {1} less to cast.
Blue spells you cast cost {1} less to cast.
Spells your opponents cast cost {1} more to cast.

Azorius Signet

Esper Sentinel

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

Wan Shi Tong, Librarian

Flash
Flying, vigilance
When Wan Shi Tong enters, put X +1/+1 counters on him. Then draw half X cards, rounded down.
Whenever an opponent searches their library, put a +1/+1 counter on Wan Shi Tong and draw a card.

Rhystic Study

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

Mana Drain

Counter target spell. At the beginning of your next main phase, add an amount of {C} equal to that spell's mana value.

Lavinia, Azorius Renegade

Each opponent can't cast noncreature spells with mana value greater than the number of lands that player controls.
Whenever an opponent casts a spell, if no mana was spent to cast it, counter that spell.

Tale's End

Counter target activated ability, triggered ability, or legendary spell.

Fractured Identity

Exile target nonland permanent. Each player other than its controller creates a token that's a copy of it.

Smothering Tithe

Whenever an opponent draws a card, that player may pay {2}. If the player doesn't, you create a Treasure token. (It's an artifact with "{T}, Sacrifice this token: Add one mana of any color.")

Summary Dismissal

Exile all other spells and counter all abilities.

An Offer You Can't Refuse

Counter target noncreature spell. Its controller creates two Treasure tokens. (They're artifacts with "{T}, Sacrifice this token: Add one mana of any color.")