Treasonous Ogre

Dethrone (Whenever this creature attacks the player with the most life or tied for most life, put a +1/+1 counter on it.)
Pay 3 life: Add {R}.

Agitator Ant

At the beginning of your end step, each player may put two +1/+1 counters on a creature they control. Goad each creature that had counters put on it this way. (Until your next turn, those creatures attack each combat if able and attack a player other than you if able.)

Undercover Butler

Whenever Undercover Butler attacks the player with the most life or tied for most life, it can't be blocked this turn.

Preacher of the Schism

Deathtouch
Whenever Preacher of the Schism attacks the player with the most life or tied for most life, create a 1/1 white Vampire creature token with lifelink.
Whenever Preacher of the Schism attacks while you have the most life or are tied for most life, you draw a card and you lose 1 life.

Marchesa, the Black Rose

Dethrone (Whenever this creature attacks the player with the most life or tied for most life, put a +1/+1 counter on it.)
Other creatures you control have dethrone.
Whenever a creature you control with a +1/+1 counter on it dies, return that card to the battlefield under your control at the beginning of the next end step.

Etali, Primal Storm

Whenever Etali, Primal Storm attacks, exile the top card of each player's library, then you may cast any number of spells from among those cards without paying their mana costs.

Marchesa's Smuggler

Dethrone (Whenever this creature attacks the player with the most life or tied for most life, put a +1/+1 counter on it.)
{1}{U}{R}: Target creature you control gains haste until end of turn and can't be blocked this turn.

Vito, Thorn of the Dusk Rose

Whenever you gain life, target opponent loses that much life.
{3}{B}{B}: Creatures you control gain lifelink until end of turn.

Guild Artisan

Commander creatures you own have "Whenever this creature attacks a player, if no opponent has more life than that player, you create two Treasure tokens." (They're artifacts with "{T}, Sacrifice this artifact: Add one mana of any color.")

Blood Tyrant

Flying, trample
At the beginning of your upkeep, each player loses 1 life. Put a +1/+1 counter on Blood Tyrant for each 1 life lost this way.
Whenever a player loses the game, put five +1/+1 counters on Blood Tyrant.

The Book of Vile Darkness

At the beginning of your end step, if you lost 2 or more life this turn, create a 2/2 black Zombie creature token.
{T}, Exile The Book of Vile Darkness and artifacts you control named Eye of Vecna and Hand of Vecna: Create Vecna, a legendary 8/8 black Zombie God creature token with indestructible and all triggered abilities of the exiled cards.

Bringer of the Last Gift

Flying
When Bringer of the Last Gift enters the battlefield, if you cast it, each player sacrifices all other creatures they control. Then each player returns all creature cards from their graveyard that weren't put there this way to the battlefield.

Blade of Selves

Equipped creature has myriad. (Whenever it attacks, for each opponent other than defending player, you may create a token copy that's tapped and attacking that player or a planeswalker they control. Exile the tokens at end of combat.)
Equip {4}

Knight of the Ebon Legion

{2}{B}: Knight of the Ebon Legion gets +3/+3 and gains deathtouch until end of turn.
At the beginning of your end step, if a player lost 4 or more life this turn, put a +1/+1 counter on Knight of the Ebon Legion. (Damage causes loss of life.)

Marchesa's Infiltrator

Dethrone (Whenever this creature attacks the player with the most life or tied for most life, put a +1/+1 counter on it.)
Whenever Marchesa's Infiltrator deals combat damage to a player, draw a card.

Sygg, River Cutthroat

At the beginning of each end step, if an opponent lost 3 or more life this turn, you may draw a card. (Damage causes loss of life.)

Scourge of the Throne

Flying
Dethrone (Whenever this creature attacks the player with the most life or tied for most life, put a +1/+1 counter on it.)
Whenever Scourge of the Throne attacks for the first time each turn, if it's attacking the player with the most life or tied for most life, untap all attacking creatures. After this phase, there is an additional combat phase.

Enraged Revolutionary

Dethrone (Whenever this creature attacks the player with the most life or tied for most life, put a +1/+1 counter on it.)

Marchesa's Emissary

Hexproof (This creature can't be the target of spells or abilities your opponents control.)
Dethrone (Whenever this creature attacks the player with the most life or tied for most life, put a +1/+1 counter on it.)

Sword Coast Sailor

Commander creatures you own have "Whenever this creature attacks a player, if no opponent has more life than that player, this creature can't be blocked this turn."

Dack's Duplicate

You may have Dack's Duplicate enter the battlefield as a copy of any creature on the battlefield, except it has haste and dethrone. (Whenever it attacks the player with the most life or tied for most life, put a +1/+1 counter on it.)

Urn of Godfire

{2}: Add one mana of any color.
{6}, {T}, Sacrifice Urn of Godfire: Destroy target creature or enchantment.

Chaos Dragon

Flying, haste
Chaos Dragon attacks each combat if able.
At the beginning of combat on your turn, each player rolls a d20. If one or more opponents had the highest result, Chaos Dragon can't attack those players or planeswalkers they control this combat.

Grenzo's Cutthroat

First strike
Dethrone (Whenever this creature attacks the player with the most life or tied for most life, put a +1/+1 counter on it.)

Whip of Erebos

Creatures you control have lifelink.
{2}{B}{B}, {T}: Return target creature card from your graveyard to the battlefield. It gains haste. Exile it at the beginning of the next end step. If it would leave the battlefield, exile it instead of putting it anywhere else. Activate only as a sorcery.