Cast Ad Nauseam by paying {3}{B}{B}.
Resolve Ad Nauseam, revealing the top card of your library, putting that card into your hand and losing life equal to that card's mana value.
Repeat the process in step 2 as many times as desired.

Infinite card draw

Ad Nauseam

Soul Echo

Activate Selenia by paying 2 life.
Repeat step 1 until you have zero life.
Resolve the first Selenia ability, returning it to your hand.
All remaining Selenia abilities fail to resolve due to no longer having a legal target.
Cast Repay in Kind by paying {5}{B}{B}, causing each opponent's life total to become zero.
Each opponent loses the game as a state-based action due to having zero or less life.

Each opponent loses the game

Near-infinite lifeloss

Selenia, Dark Angel

Repay in Kind

At the beginning of your upkeep, Axis of Mortality triggers.
Activate Necropotence by paying 1 life, exiling the top card of your library face down.
Repeat step 2 until you have zero life.
Resolve the Axis of Mortality trigger, swapping your life total with an opponent.
The opponent loses the game due to having zero life.
You may repeat this on each of your turns.

Target player loses the game on each of your turns

Axis of Mortality

Necropotence

At the beginning of your upkeep, Axis of Mortality triggers.
Activate Wall of Blood by paying 1 life, giving Wall of Blood +1/+1 until end of turn.
Repeat step 2 until you have zero life.
Resolve the Axis of Mortality trigger, swapping your life total with an opponent.
The opponent loses the game due to having zero life.
You may repeat this on each of your turns.

Wall of Blood

Activate Wall of Blood by paying 1 life, giving Wall of Blood +1/+1 until end of turn.
Repeat step 1 until you have zero life.
Activate Soul Conduit by paying {6} and tapping it, exchanging your life total with an opponent's.
The opponent loses the game due to having zero life.
You may repeat this on each of your turns.

Soul Conduit

Activate Necropotence by paying 1 life, exiling the top card of your library face down.
Repeat step 1 until you have zero life.
Activate Soul Conduit by paying {6} and tapping it, exchanging your life total with an opponent's.
The opponent loses the game due to having zero life.
You may repeat this on each of your turns.

During your upkeep, activate Wall of Blood by paying 1 life, giving Wall of Blood +1/+1 until end of turn.
Repeat step 1 until you have zero life.
Activate Magus of the Mirror by tapping and sacrificing it, exchanging your life total with an opponent.
The opponent loses the game due to having zero life.

Target player loses the game

Magus of the Mirror

During your upkeep, activate Necropotence by paying 1 life, exiling the top card of your library face down.
Repeat step 1 until you have zero life.
Activate Magus of the Mirror by tapping and sacrificing it, exchanging your life total with an opponent.
The opponent loses the game due to having zero life.

At the beginning of your upkeep, Axis of Mortality triggers.
Activate Blood Celebrant by paying {B} and one life, adding {B}.
Repeat step 2 until you have zero life.
Resolve the Axis of Mortality trigger, swapping your life total with an opponent.
The opponent loses the game due to having zero life.
You may repeat this on each of your turns.

Blood Celebrant

Activate Blood Celebrant by paying {B} and one life, adding {B}.
Repeat step 1 until you have zero life.
Activate Soul Conduit by paying {6} and tapping it, exchanging your life total with an opponent's.
The opponent loses the game due to having zero life.
You may repeat this on each of your turns.

During your upkeep, activate Blood Celebrant by paying {B} and one life, adding {B}.
Repeat step 1 until you have zero life.
Activate Magus of the Mirror by tapping and sacrificing it, exchanging your life total with an opponent.
The opponent loses the game due to having zero life.

At the beginning of your upkeep, Axis of Mortality triggers.
Activate Ethereal Champion by paying 1 life, preventing the next one damage that will be dealt to Ethereal Champion this turn.
Repeat step 2 until you have zero life.
Resolve the Axis of Mortality trigger, swapping your life total with an opponent.
The opponent loses the game due to having zero life.
You may repeat this on each of your turns.

Ethereal Champion

Activate Ethereal Champion by paying 1 life, preventing the next one damage that will be dealt to Ethereal Champion this turn.
Repeat step 1 until you have zero life.
Activate Soul Conduit by paying {6} and tapping it, exchanging your life total with an opponent's.
The opponent loses the game due to having zero life.
You may repeat this on each of your turns.

During your upkeep, activate Ethereal Champion by paying 1 life, preventing the next one damage that will be dealt to Ethereal Champion this turn.
Repeat step 1 until you have zero life.
Activate Magus of the Mirror by tapping and sacrificing it, exchanging your life total with an opponent.
The opponent loses the game due to having zero life.

During your upkeep, activate Cavern Harpy by paying 1 life.
Repeat step 1 until you have zero life.
Resolve the last Cavern Harpy trigger, returning it to your hand.
The remaining Cavern Harpy triggers fizzle.
Activate Magus of the Mirror by tapping and sacrificing it, exchanging your life total with an opponent.
The opponent loses the game due to having zero life.

Cavern Harpy

At the beginning of your upkeep, Axis of Mortality triggers.
Activate Cavern Harpy by paying 1 life.
Repeat step 2 until you have zero life.
Resolve the last Cavern Harpy trigger, returning it to your hand.
The remaining Cavern Harpy triggers fizzle.
Resolve the Axis of Mortality trigger, swapping your life total with an opponent.
The opponent loses the game due to having zero life.
You may repeat this on each of your turns.

Activate Cavern Harpy by paying 1 life.
Repeat step 1 until you have zero life.
Resolve the last Cavern Harpy trigger, returning it to your hand.
The remaining Cavern Harpy triggers fizzle.
Activate Soul Conduit by paying {6} and tapping it, exchanging your life total with an opponent's.
The opponent loses the game due to having zero life.
You may repeat this on each of your turns.

Combos with "Soul Echo"