Herald of Leshrac

Flying
Cumulative upkeep—Gain control of a land you don't control. (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.)
Herald of Leshrac gets +1/+1 for each land you control but don't own.
When Herald of Leshrac leaves the battlefield, each player gains control of each land they own that you control.

Beledros Witherbloom

Flying
At the beginning of each upkeep, create a 1/1 black and green Pest creature token with "When this creature dies, you gain 1 life."
Pay 10 life: Untap all lands you control. Activate only once each turn.

Platinum Angel

Flying
You can't lose the game and your opponents can't win the game.

Peer into the Abyss

Target player draws cards equal to half the number of cards in their library and loses half their life. Round up each time.

Belbe, Corrupted Observer

At the beginning of each postcombat main phase, the active player adds {C}{C} for each of your opponents who lost life this turn. (Damage causes loss of life.)

Exsanguinate

Each opponent loses X life. You gain life equal to the life lost this way.

Price of Knowledge

Players have no maximum hand size.
At the beginning of each opponent's upkeep, Price of Knowledge deals damage to that player equal to the number of cards in that player's hand.

Sins of the Past

Until end of turn, you may cast target instant or sorcery card from your graveyard without paying its mana cost. If that spell would be put into your graveyard, exile it instead. Exile Sins of the Past.

Mindslaver

{4}, {T}, Sacrifice Mindslaver: You control target player during that player's next turn. (You see all cards that player could see and make all decisions for the player.)

Choice of Damnations

Target opponent chooses a number. You may have that player lose that much life. If you don't, that player sacrifices all but that many permanents of their choice.

Plague Wind

Destroy all creatures you don't control. They can't be regenerated.

Cruel Entertainment

Choose target player and another target player. The first player controls the second player during the second player's next turn, and the second player controls the first player during the first player's next turn.