Activate Mischievous Poltergeist by paying life.
Repeat step 1 as desired.
Activate Rowan by tapping it, reducing the cost of all black and/or red spells you cast this turn.
Cast Exsanguinate, choosing for X to equal the amount of life you've lost this turn, but paying a total of {B}{B} due to Rowan.
Resolve Exsanguinate, causing each opponent to lose X life, and you to gain life equal to the life lost this way.

Near-infinite lifegain

Near-infinite lifeloss

Rowan, Scion of War

Exsanguinate

Mischievous Poltergeist

Activate Mischievous Poltergeist by paying 1 life.
Repeat step 1 until you have 0 life.
Resolve all Mischievous Poltergeist abilities.
Cast Repay in Kind by paying {5}{B}{B}, causing each opponent's life total to become 0.
Each opponent loses the game as a state-based action due to having 0 life.

Each opponent loses the game

Near-infinite lifeloss for all players

Permanent with "You don't lose the game due to having 0 or less life"

Repay in Kind

Activate Mischievous Poltergeist by paying 1 life.
Vilis triggers, causing you to draw a card.
Sheoldred's first ability triggers, causing you to gain 2 life.
Repeat as desired.
Resolve all Mischievous Poltergeist abilities.

Infinite card draw

Infinite draw triggers

Near-infinite lifegain triggers

Sheoldred, the Apocalypse

Vilis, Broker of Blood

Activate Vizkopa Guildmage's second ability by paying {1}{W}{B}, causing each opponent to lose life whenever you gain life this turn.
Activate Mischievous Poltergeist by paying 1 life.
Repeat step 2 until you have 1 life.
Activate Children of Korils by sacrificing it, causing you to gain life equal to the amount of life you've lost this turn.
Vizkopa Guildmage triggers, causing each opponent to lose life equal to the amount of life you gained.

Children of Korlis

Vizkopa Guildmage

Activate Vizkopa Guildmage by paying {1}{W}{B}, causing each opponent to lose life whenever you gain life this turn.
Activate Mischievous Poltergeist by paying 1 life, regenerating it.
Repeat step 2 until you have one life.
Cast Oketra's Last Mercy by paying {1}{W}{W}, causing your life total to become forty.
Vizkopa Guildmage triggers, causing each opponent to lose thirty-nine life.
Each opponent loses the game due to having zero or less life.

Oketra's Last Mercy

Activate Mischievous Poltergeist by paying 1 life.
Repeat step 1 until Greven has power 21 or greater due to its first ability.
Deal combat damage to an opponent using Greven. The opponent loses the game due to being dealt 21 or more combat damage from your commander.

Target opponent loses the game

Greven, Predator Captain

Activate Mischievous Poltergeist by paying life.
Repeat step 1 as desired.
Activate Rowan by tapping it, reducing the cost of all black and/or red spells you cast this turn.
Cast a copy of Exsanguinate, choosing for X to equal the amount of life you've lost this turn, but paying a total of {B}{B} due to Rowan.
Resolve Exsanguinate, causing each opponent to lose X life, and you to gain life equal to the life lost this way.

Combos with "Mischievous Poltergeist"