Lore Seeker

At the beginning of your upkeep, you may say "Ach! Hans, run! It's the . . ." and the name of a creature card. If you do, search your library for a card with that name, put it onto the battlefield, then shuffle your library. That creature gains haste. Exile it at the beginning of the next end step.

{3}{B}, Exile a permanent you control with a League of Dastardly Doom watermark: Return a permanent card with a League of Dastardly Doom watermark from your graveyard to the battlefield.

Whenever a creature an opponent controls becomes tapped, that creature doesn't untap during its controller's next untap step.

When you set this scheme in motion, until your next turn, whenever a player taps a land for mana, that player adds one mana of any type that land produced.

Spells and abilities you control can't destroy, exile, target, or cause you to sacrifice A Good Thing.
At the beginning of your upkeep, double your life total. Then, if you have 1,000 or more life, you lose the game.

When you set this scheme in motion, look at the top six cards of your library. You may put a creature card from among them onto the battlefield. Put the rest on the bottom of your library in any order.

Whenever a face-down creature you control deals combat damage to an opponent, you may exile it, then cast it without paying its mana cost.
{2}{R}{R}: Put a card from your hand onto the battlefield face down.

Target player puts the top three cards of their library into their graveyard.
Decipher {6}{U}

Counter target spell. If that spell is countered this way, put it on the bottom of its owner's library instead of into their graveyard.

Two target creatures you control gain indestructible until end of turn.

Exile target attacking creature. Then remove it from the game. Then put it into the absolutely-removed-from-the-freaking-game-forever zone.

Up to two target creatures each get +1/+0 and gain first strike until end of turn.
Madness {1}{R}

{T}: Each opponent puts the top card of their library into their graveyard.
{3}, {T}: Exile three target cards from an opponent's graveyard. Draw a card.

When Abandoned Bonfire enters the battlefield, you gain 2 life.
{T}: Add {C}.

Abandoned Excavation enters the battlefield with a charge counter on it.
{T}: Add {C}.
{T}, Remove a charge counter from Abandoned Excavation: Add one mana of any color.

You may cast spells that have a cycling ability from your graveyard.
If a card that has a cycling ability would be put into your graveyard from anywhere and it wasn't cycled, exile it instead.

First strike
Whenever a creature dealt damage by Abattoir Ghoul this turn dies, you gain life equal to that creature's toughness.

Frenzy 2
Whenever Abberrant Idealon becomes blocked, distribute two -1/-1 counters among one or two creatures defending player controls.

Flying, vigilance

Prowess
When Abbot of Keral Keep enters the battlefield, exile the top card of your library. Until end of turn, you may play that card.

Flying
At the beginning of your upkeep, mill a card. If an instant or sorcery card was milled this way, transform Aberrant Researcher.

Flying
When Abhorrent Overlord enters the battlefield, create a number of 1/1 black Harpy creature tokens with flying equal to your devotion to black.
At the beginning of your upkeep, sacrifice a creature.

As Abian, Luvion Usurper enters the battlefield, you become Abian. (Your life total becomes equal to their loyalty. You can activate the loyalty abilities by spending or gaining life.)
[+3]: Discard your hand, then draw cards equal to the greatest power among creatures you control.
[+1]: Create a 3/2 red and green Spirit creature token.
[–X]: You deal X damage to any target.

Whenever Abigail, Cawyer Station Chief enters the battlefield or one or more nontoken creatures you control deal combat damage to a player, create a 2/2 white Soldier creature token.
{R}, Sacrifice a token: Abigail, Cawyer Station Chief deals 1 damage to target creature. That creature can't block this turn.

Until end of turn, target creature gets +2/+0 and gains "When this creature dies, return it to the battlefield tapped under its owner's control."