Willbreaker

Whenever a creature an opponent controls becomes the target of a spell or ability you control, gain control of that creature for as long as you control Willbreaker.

Entrancing Melody

Gain control of target creature with mana value X.

Aura Graft

Gain control of target Aura that's attached to a permanent. Attach it to another permanent it can enchant.

Mind Flayer

Dominate Monster — When Mind Flayer enters, gain control of target creature for as long as you control Mind Flayer.

Agent of Treachery

When Agent of Treachery enters, gain control of target permanent.
At the beginning of your end step, if you control three or more permanents you don't own, draw three cards.

Commandeer

You may exile two blue cards from your hand rather than pay this spell's mana cost.
Gain control of target noncreature spell. You may choose new targets for it. (If that spell is an artifact, enchantment, or planeswalker, the permanent enters under your control.)

Mass Manipulation

Gain control of X target creatures and/or planeswalkers.

Island

Blatant Thievery

For each opponent, gain control of target permanent that player controls.

Thieving Skydiver

Kicker {X}. X can't be 0. (You may pay an additional {X} as you cast this spell.)
Flying
When Thieving Skydiver enters, if it was kicked, gain control of target artifact with mana value X or less. If that artifact is an Equipment, attach it to Thieving Skydiver.

Keiga, the Tide Star

Flying
When Keiga, the Tide Star dies, gain control of target creature.

Flayer of Loyalties

When you cast this spell, gain control of target creature until end of turn. Untap that creature. Until end of turn, it has base power and toughness 10/10 and gains trample, annihilator 2, and haste.
Annihilator 2 (Whenever this creature attacks, defending player sacrifices two permanents of their choice.)
Trample

Shield Broker

When Shield Broker enters, put a shield counter on target noncommander creature you don't control. You gain control of that creature for as long as it has a shield counter on it. (If it would be dealt damage or destroyed, remove a shield counter from it instead.)

Jace, Ingenious Mind-Mage

+1: Draw a card.
+1: Untap all creatures you control.
−9: Gain control of up to three target creatures.

Aethersnatch

Gain control of target spell. You may choose new targets for it. (If that spell becomes a permanent, it enters under your control.)

Beguiler of Wills

{T}: Gain control of target creature with power less than or equal to the number of creatures you control.

Blue Sun's Twilight

Gain control of target creature with mana value X or less. If X is 5 or more, create a token that's a copy of that creature.