Kitesail Larcenist

Flying, ward {1}
When this creature enters, for each player, choose up to one other target artifact or creature that player controls. For as long as this creature remains on the battlefield, the chosen permanents become Treasure artifacts with "{T}, Sacrifice this artifact: Add one mana of any color" and lose all other abilities.

Faerie Mastermind

Flash
Flying
Whenever an opponent draws their second card each turn, you draw a card.
{3}{U}: Each player draws a card.

Vein Ripper

Flying
Ward—Sacrifice a creature.
Whenever a creature dies, target opponent loses 2 life and you gain 2 life.

Double Down

Whenever you cast an outlaw spell, copy that spell. (Assassins, Mercenaries, Pirates, Rogues, and Warlocks are outlaws. Copies of permanent spells become tokens.)

Aven Heartstabber

Flying
As long as there are five or more mana values among cards in your graveyard, this creature gets +2/+2 and has deathtouch.
When this creature dies, mill two cards, then draw a card.

Undercover Operative

You may have this creature enter as a copy of any creature on the battlefield, except it enters with a shield counter on it if you control that creature. (If it would be dealt damage or destroyed, remove a shield counter from it instead.)

Spyglass Siren

Flying
When this creature enters, create a Map token. (It's an artifact with "{1}, {T}, Sacrifice this token: Target creature you control explores. Activate only as a sorcery.")

Hellspur Posse Boss

Other outlaws you control have haste. (Assassins, Mercenaries, Pirates, Rogues, and Warlocks are outlaws.)
When this creature enters, create two 1/1 red Mercenary creature tokens with "{T}: Target creature you control gets +1/+0 until end of turn. Activate only as a sorcery."

Hostile Investigator

When this creature enters, target opponent discards a card.
Whenever one or more players discard one or more cards, investigate. This ability triggers only once each turn. (Create a Clue token. It's an artifact with "{2}, Sacrifice this token: Draw a card.")