Merieke Ri Berit

Merieke Ri Berit doesn't untap during your untap step.
{T}: Gain control of target creature for as long as you control Merieke Ri Berit. When Merieke Ri Berit leaves the battlefield or becomes untapped, destroy that creature. It can't be regenerated.

Freed from the Real

Enchant creature
{U}: Tap enchanted creature.
{U}: Untap enchanted creature.

Ghosthelm Courier

You may choose not to untap Ghosthelm Courier during your untap step.
{2}{U}, {T}: Target Wizard creature gets +2/+2 and has shroud for as long as Ghosthelm Courier remains tapped. (It can't be the target of spells or abilities.)

Amber Prison

You may choose not to untap Amber Prison during your untap step.
{4}, {T}: Tap target artifact, creature, or land. That permanent doesn't untap during its controller's untap step for as long as Amber Prison remains tapped.

Imi Statue

Players can't untap more than one artifact during their untap steps.

Thornbite Staff

Equipped creature has "{2}, {T}: This creature deals 1 damage to any target" and "Whenever a creature dies, untap this creature."
Whenever a Shaman creature enters the battlefield, you may attach Thornbite Staff to it.
Equip {4}

Thalakos Dreamsower

Shadow (This creature can block or be blocked by only creatures with shadow.)
You may choose not to untap Thalakos Dreamsower during your untap step.
Whenever Thalakos Dreamsower deals damage to an opponent, tap target creature. That creature doesn't untap during its controller's untap step for as long as Thalakos Dreamsower remains tapped.

Thran Weaponry

Echo {4} (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.)
You may choose not to untap Thran Weaponry during your untap step.
{2}, {T}: All creatures get +2/+2 for as long as Thran Weaponry remains tapped.

Captain of the Mists

Whenever another Human enters the battlefield under your control, untap Captain of the Mists.
{1}{U}, {T}: You may tap or untap target permanent.

Old Man of the Sea

You may choose not to untap Old Man of the Sea during your untap step.
{T}: Gain control of target creature with power less than or equal to Old Man of the Sea's power for as long as Old Man of the Sea remains tapped and that creature's power remains less than or equal to Old Man of the Sea's power.

Ice Floe

You may choose not to untap Ice Floe during your untap step.
{T}: Tap target creature without flying that's attacking you. It doesn't untap during its controller's untap step for as long as Ice Floe remains tapped.

Ashnod's Battle Gear

You may choose not to untap Ashnod's Battle Gear during your untap step.
{2}, {T}: Target creature you control gets +2/-2 for as long as Ashnod's Battle Gear remains tapped.

Tawnos's Coffin

You may choose not to untap Tawnos's Coffin during your untap step.
{3}, {T}: Exile target creature and all Auras attached to it. Note the number and kind of counters that were on that creature. When Tawnos's Coffin leaves the battlefield or becomes untapped, return that exiled card to the battlefield under its owner's control tapped with the noted number and kind of counters on it. If you do, return the other exiled cards to the battlefield under their owner's control attached to that permanent.

Arcane Lighthouse

{T}: Add {C}.
{1}, {T}: Until end of turn, creatures your opponents control lose hexproof and shroud and can't have hexproof or shroud.

Pearlspear Courier

You may choose not to untap Pearlspear Courier during your untap step.
{2}{W}, {T}: Target Soldier creature gets +2/+2 and has vigilance for as long as Pearlspear Courier remains tapped.

Seasinger

When you control no Islands, sacrifice Seasinger.
You may choose not to untap Seasinger during your untap step.
{T}: Gain control of target creature whose controller controls an Island for as long as you control Seasinger and Seasinger remains tapped.

Stasis

Players skip their untap steps.
At the beginning of your upkeep, sacrifice Stasis unless you pay {U}.

Hisoka's Guard

You may choose not to untap Hisoka's Guard during your untap step.
{1}{U}, {T}: Target creature you control other than Hisoka's Guard has shroud for as long as Hisoka's Guard remains tapped. (It can't be the target of spells or abilities.)

Kill Switch

{2}, {T}: Tap all other artifacts. They don't untap during their controllers' untap steps for as long as Kill Switch remains tapped.

Plains

Giant Oyster

You may choose not to untap Giant Oyster during your untap step.
{T}: For as long as Giant Oyster remains tapped, target tapped creature doesn't untap during its controller's untap step, and at the beginning of each of your draw steps, put a -1/-1 counter on that creature. When Giant Oyster leaves the battlefield or becomes untapped, remove all -1/-1 counters from the creature.

Storage Matrix

As long as Storage Matrix is untapped, each player chooses artifact, creature, or land during their untap step. That player can untap only permanents of the chosen type this step.

Rust Tick

You may choose not to untap Rust Tick during your untap step.
{1}, {T}: Tap target artifact. It doesn't untap during its controller's untap step for as long as Rust Tick remains tapped.

Swamp

Tawnos's Weaponry

You may choose not to untap Tawnos's Weaponry during your untap step.
{2}, {T}: Target creature gets +1/+1 for as long as Tawnos's Weaponry remains tapped.

Throne of the God-Pharaoh

At the beginning of your end step, each opponent loses life equal to the number of tapped creatures you control.

Callous Oppressor

You may choose not to untap Callous Oppressor during your untap step.
As Callous Oppressor enters the battlefield, an opponent chooses a creature type.
{T}: Gain control of target creature that isn't of the chosen type for as long as Callous Oppressor remains tapped.

Hidden Strings

You may tap or untap target permanent, then you may tap or untap another target permanent.
Cipher (Then you may exile this spell card encoded on a creature you control. Whenever that creature deals combat damage to a player, its controller may cast a copy of the encoded card without paying its mana cost.)

Damping Field

Entrancing Lyre

You may choose not to untap Entrancing Lyre during your untap step.
{X}, {T}: Tap target creature with power X or less. It doesn't untap during its controller's untap step for as long as Entrancing Lyre remains tapped.

Howling Mine

At the beginning of each player's draw step, if Howling Mine is untapped, that player draws an additional card.

Static Orb

As long as Static Orb is untapped, players can't untap more than two permanents during their untap steps.

Spirit Shield

You may choose not to untap Spirit Shield during your untap step.
{2}, {T}: Target creature gets +0/+2 for as long as Spirit Shield remains tapped.

Retreat to Coralhelm

Landfall — Whenever a land enters the battlefield under your control, choose one —
• You may tap or untap target creature.
• Scry 1. (Look at the top card of your library. You may put that card on the bottom of your library.)

Mana Leech

You may choose not to untap Mana Leech during your untap step.
{T}: Tap target land. It doesn't untap during its controller's untap step for as long as Mana Leech remains tapped.

Stinging Lionfish

Whenever you cast your first spell during each opponent's turn, you may tap or untap target nonland permanent.

Ghostly Touch

Enchant creature
Enchanted creature has "Whenever this creature attacks, you may tap or untap target permanent."

Endoskeleton

You may choose not to untap Endoskeleton during your untap step.
{2}, {T}: Target creature gets +0/+3 for as long as Endoskeleton remains tapped.

Genesis Chamber

Whenever a nontoken creature enters the battlefield, if Genesis Chamber is untapped, that creature's controller creates a 1/1 colorless Myr artifact creature token.

Phyrexian Gremlins

You may choose not to untap Phyrexian Gremlins during your untap step.
{T}: Tap target artifact. It doesn't untap during its controller's untap step for as long as Phyrexian Gremlins remains tapped.

Masako the Humorless

Flash
Tapped creatures you control can block as though they were untapped.

Detection Tower

{T}: Add {C}.
{1}, {T}: Until end of turn, your opponents and creatures your opponents control with hexproof can be the targets of spells and abilities you control as though they didn't have hexproof.

Stonybrook Angler

{1}{U}, {T}: You may tap or untap target creature.

Chain Stasis

You may tap or untap target creature. Then that creature's controller may pay {2}{U}. If the player does, they may copy this spell and may choose a new target for that copy.

Preacher

You may choose not to untap Preacher during your untap step.
{T}: For as long as Preacher remains tapped, gain control of target creature of an opponent's choice they control.

Island

Pemmin's Aura

Enchant creature
{U}: Untap enchanted creature.
{U}: Enchanted creature gains flying until end of turn.
{U}: Enchanted creature gains shroud until end of turn. (It can't be the target of spells or abilities.)
{1}: Enchanted creature gets +1/-1 or -1/+1 until end of turn.

Teferi, Temporal Archmage

+1: Look at the top two cards of your library. Put one of them into your hand and the other on the bottom of your library.
−1: Untap up to four target permanents.
−10: You get an emblem with "You may activate loyalty abilities of planeswalkers you control on any player's turn any time you could cast an instant."
Teferi, Temporal Archmage can be your commander.

Mind Over Matter

Discard a card: You may tap or untap target artifact, creature, or land.

Illusionist's Bracers

Whenever an ability of equipped creature is activated, if it isn't a mana ability, copy that ability. You may choose new targets for the copy.
Equip {3}

Tideforce Elemental

{U}, {T}: You may tap or untap another target creature.
Landfall — Whenever a land enters the battlefield under your control, you may untap Tideforce Elemental.

Dream Tides

Creatures don't untap during their controllers' untap steps.
At the beginning of each player's upkeep, that player may choose any number of tapped nongreen creatures they control and pay {2} for each creature chosen this way. If the player does, untap those creatures.

Sphinx Sovereign

Flying
At the beginning of your end step, you gain 3 life if Sphinx Sovereign is untapped. Otherwise, each opponent loses 3 life.

Vedalken Shackles

You may choose not to untap Vedalken Shackles during your untap step.
{2}, {T}: Gain control of target creature with power less than or equal to the number of Islands you control for as long as Vedalken Shackles remains tapped.

Mole Worms

You may choose not to untap Mole Worms during your untap step.
{T}: Tap target land. It doesn't untap during its controller's untap step for as long as Mole Worms remains tapped.

Tidal Force

At the beginning of each upkeep, you may tap or untap target permanent.

Fatestitcher

{T}: You may tap or untap another target permanent.
Unearth {U} ({U}: Return this card from your graveyard to the battlefield. It gains haste. Exile it at the beginning of the next end step or if it would leave the battlefield. Unearth only as a sorcery.)

Sand Squid

Islandwalk (This creature can't be blocked as long as defending player controls an Island.)
You may choose not to untap Sand Squid during your untap step.
{T}: Tap target creature. That creature doesn't untap during its controller's untap step for as long as Sand Squid remains tapped.

Tolarian Kraken

Whenever you draw a card, you may pay {1}. When you do, you may tap or untap target creature.

Helm of Possession

You may choose not to untap Helm of Possession during your untap step.
{2}, {T}, Sacrifice a creature: Gain control of target creature for as long as you control Helm of Possession and Helm of Possession remains tapped.

Deserter's Quarters

You may choose not to untap Deserter's Quarters during your untap step.
{6}, {T}: Tap target creature. It doesn't untap during its controller's untap step for as long as Deserter's Quarters remains tapped.

Mesmeric Orb

Whenever a permanent becomes untapped, that permanent's controller mills a card.

Dragonscale General

At the beginning of your end step, bolster X, where X is the number of tapped creatures you control. (Choose a creature with the least toughness among creatures you control and put X +1/+1 counters on it.)

Energy Arc

Untap any number of target creatures. Prevent all combat damage that would be dealt to and dealt by those creatures this turn.

Reins of Power

Untap all creatures you control and all creatures target opponent controls. You and that opponent each gain control of all creatures the other controls until end of turn. Those creatures gain haste until end of turn.

Niblis of the Breath

Flying
{U}, {T}: You may tap or untap target creature.

Zelyon Sword

You may choose not to untap Zelyon Sword during your untap step.
{3}, {T}: Target creature gets +2/+0 for as long as Zelyon Sword remains tapped.

Frightshroud Courier

You may choose not to untap Frightshroud Courier during your untap step.
{2}{B}, {T}: Target Zombie creature gets +2/+2 and has fear for as long as Frightshroud Courier remains tapped. (It can't be blocked except by artifact creatures and/or black creatures.)

Flowstone Armor

You may choose not to untap Flowstone Armor during your untap step.
{3}, {T}: Target creature gets +1/-1 for as long as Flowstone Armor remains tapped.