Activate Field of Ruin's second ability by paying {2}, tapping and sacrificing it, targeting any nonbasic land an opponent controls.
Holding priority, cast Radiant Performer by paying {3}{R}{R}.
When Radiant Performer enters the battlefield, it triggers, copying Field of Ruin's ability for each other nonbasic land your opponents control.
Resolve the first Field of Ruin ability, destroying the land it it targeting, then causing each player to search their library for a basic land card and put it onto the battlefield.
River Song triggers for each opponent who searches this way.
Resolve the first trigger, putting a +1/+1 counter on it and dealing damage equal to its power to an opponent.
Repeat step 6 for each other trigger.
Repeat from step 4 for each other Field of Ruin ability.

Near-infinite damage

River Song

Radiant Performer

Field of Ruin

Activate Door to Nothingness by paying {W}{W}{U}{U}{B}{B}{R}{R}{G}{G} and tapping it, targeting yourself.
Holding priority, cast Radiant Performer by paying {3}{R}{R}.
Radiant Performer enters the battlefield, copying Door to Nothingness' ability for each opponent.
Resolve each copy of Door to Nothingness' ability, causing each opponent to lose the game.

Each opponent loses the game

Door to Nothingness

Cast Confiscate by {4}{U}{U}, targeting any permanent on the battlefield.
Holding priority, cast Radiant Performer by paying {3}{R}{R}.
Radiant Performer enters the battlefield, creating a copy of Confiscate for each other permanent on the battlefield.
Resolve each Confiscate, causing you to gain control of all permanents.

Mass Land Denial

Gain control of all permanents

Confiscate

Cast Lay Claim by {5}{U}{U}, targeting any permanent on the battlefield.
Holding priority, cast Radiant Performer by paying {3}{R}{R}.
Radiant Performer enters the battlefield, creating a copy of Lay Claim for each other permanent on the battlefield.
Resolve each Lay Claim, causing you to gain control of all permanents.

Lay Claim

Activate Field of Ruin's second ability by paying {2}, tapping and sacrificing it, targeting any nonbasic land an opponent controls.
Holding priority, cast Radiant Performer by paying {3}{R}{R}.
When Radiant Performer enters the battlefield, it triggers, copying Field of Ruin's ability for each other nonbasic land your opponents control.
Resolve the first Field of Ruin ability, destroying the land it it targeting, then causing each player to search their library for a basic land card and put it onto the battlefield.
Ob Nixilis' first ability triggers for each opponent who searches this way, causing each opponent to sacrifice a creature and lose 10 life.
Repeat from step 4 for each other Field of Ruin ability.

Near-infinite lifeloss

Ob Nixilis, Unshackled

Cast Volition Reins by {3}{U}{U}{U}, targeting any permanent on the battlefield.
Holding priority, cast Radiant Performer by paying {3}{R}{R}.
Radiant Performer enters the battlefield, creating a copy of Volition Reins for each other permanent on the battlefield.
Resolve each Volition Reins, causing you to gain control of all permanents.

Volition Reins

Cast In Bolas's Clutches by {4}{U}{U}, targeting any permanent on the battlefield.
Holding priority, cast Radiant Performer by paying {3}{R}{R}.
Radiant Performer enters the battlefield, creating a copy of In Bolas's Clutches for each other permanent on the battlefield.
Resolve each In Bolas's Clutches, causing you to gain control of all permanents.

Combos with "Radiant Performer"