Hallowed Fountain

({T}: Add {W} or {U}.)
As Hallowed Fountain enters, you may pay 2 life. If you don't, it enters tapped.

Leonin Arbiter

Players can't search libraries. Any player may pay {2} for that player to ignore this effect until end of turn.

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 artifact: Add one mana of any color.")

Mana Crypt

At the beginning of your upkeep, flip a coin. If you lose the flip, Mana Crypt deals 3 damage to you.
{T}: Add {C}{C}.

Teferi, Hero of Dominaria

+1: Draw a card. At the beginning of the next end step, untap up to two lands.
−3: Put target nonland permanent into its owner's library third from the top.
−8: You get an emblem with "Whenever you draw a card, exile target permanent an opponent controls."

Sol Ring

Thalia, Heretic Cathar

First strike
Creatures and nonbasic lands your opponents control enter tapped.

Knowledge Pool

Imprint — When Knowledge Pool enters, each player exiles the top three cards of their library.
Whenever a player casts a spell from their hand, that player exiles it. If the player does, they may cast a spell from among other cards exiled with Knowledge Pool without paying its mana cost.

Ghostly Prison

Creatures can't attack you unless their controller pays {2} for each creature they control that's attacking you.

Blind Obedience

Extort (Whenever you cast a spell, you may pay {W/B}. If you do, each opponent loses 1 life and you gain that much life.)
Artifacts and creatures your opponents control enter tapped.

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.

Containment Priest

Flash
If a nontoken creature would enter and it wasn't cast, exile it instead.

Rhystic Study

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

Aven Mindcensor

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

Sphere of Safety

Creatures can't attack you or planeswalkers you control unless their controller pays {X} for each of those creatures, where X is the number of enchantments you control.

Omen Machine

Players can't draw cards.
At the beginning of each player's draw step, that player exiles the top card of their library. If it's a land card, the player puts it onto the battlefield. Otherwise, the player casts it without paying its mana cost if able.

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.