Umbilicus

At the beginning of each player's upkeep, that player may pay 2 life. If they don't, they return a permanent they control to its owner's hand.

Custody Battle

Enchant creature
Enchanted creature has "At the beginning of your upkeep, target opponent gains control of this creature unless you sacrifice a land."

Isolation Cell

Whenever an opponent casts a creature spell, that player loses 2 life unless they pay {2}.

Ogre Enforcer

Ogre Enforcer can't be destroyed by lethal damage unless lethal damage dealt by a single source is marked on it.

Sirocco

Target player reveals their hand. For each blue instant card revealed this way, that player discards that card unless they pay 4 life.

Erratic Portal

{1}, {T}: Return target creature to its owner's hand unless its controller pays {1}.

Skullscorch

Target player discards two cards at random unless that player has Skullscorch deal 4 damage to them.

Molten Influence

Counter target instant or sorcery spell unless its controller has Molten Influence deal 4 damage to them.

Enchanter's Bane

At the beginning of your end step, target enchantment deals damage equal to its mana value to its controller unless that player sacrifices it.

Kazuul, Tyrant of the Cliffs

Whenever a creature an opponent controls attacks, if you're the defending player, create a 3/3 red Ogre creature token unless that creature's controller pays {3}.

Barbarian Bully

Discard a card at random: Barbarian Bully gets +2/+2 until end of turn unless a player has Barbarian Bully deal 4 damage to them. Activate only once each turn.

Avalanche Riders

Haste
Echo {3}{R} (At the beginning of your upkeep, if this came under your control since the beginning of your last upkeep, sacrifice it unless you pay its echo cost.)
When Avalanche Riders enters, destroy target land.

Skullcage

At the beginning of each opponent's upkeep, Skullcage deals 2 damage to that player unless they have exactly three or exactly four cards in hand.

Instill Furor

Enchant creature
Enchanted creature has "At the beginning of your end step, sacrifice this creature unless it attacked this turn."

Blood Clock

At the beginning of each player's upkeep, that player returns a permanent they control to its owner's hand unless they pay 2 life.

Amulet of Safekeeping

Whenever you become the target of a spell or ability an opponent controls, counter that spell or ability unless its controller pays {1}.
Creature tokens get -1/-0.

Demanding Dragon

Flying
When Demanding Dragon enters, it deals 5 damage to target opponent unless that player sacrifices a creature of their choice.

Reality Smasher

({C} represents colorless mana.)
Trample, haste
Whenever Reality Smasher becomes the target of a spell an opponent controls, counter that spell unless its controller discards a card.

Heart of Bogardan

Cumulative upkeep {2} (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.)
When a player doesn't pay Heart of Bogardan's cumulative upkeep, Heart of Bogardan deals X damage to target player or planeswalker and each creature that player or that planeswalker's controller controls, where X is twice the number of age counters on Heart of Bogardan minus 2.

Blazing Salvo

Blazing Salvo deals 3 damage to target creature unless that creature's controller has Blazing Salvo deal 5 damage to them.

Lava Blister

Destroy target nonbasic land unless its controller has Lava Blister deal 6 damage to them.

War Cadence

{X}{R}: This turn, creatures can't block unless their controller pays {X} for each blocking creature they control.

Crimson Honor Guard

Trample
At the beginning of each player's end step, Crimson Honor Guard deals 4 damage to that player unless they control a commander.

Rhystic Cave

{T}: Choose a color. Add one mana of that color unless any player pays {1}. Activate only as an instant.

Rhystic Lightning

Rhystic Lightning deals 4 damage to any target unless that permanent's controller or that player pays {2}. If they do, Rhystic Lightning deals 2 damage to the permanent or player.

Pia's Revolution

Whenever a nontoken artifact is put into your graveyard from the battlefield, return that card to your hand unless target opponent has Pia's Revolution deal 3 damage to them.

Dwarven Scorcher

Sacrifice Dwarven Scorcher: Dwarven Scorcher deals 1 damage to target creature unless that creature's controller has Dwarven Scorcher deal 2 damage to them.

Dwarven Driller

{T}: Destroy target land unless its controller has Dwarven Driller deal 2 damage to them.