Cast Massacre Wurm by paying {3}{B}{B}{B}.
When Massacre Wurm enters, it's first ability triggers, giving all opposing creatures -2/-2 until end of turn.
All of your opponents' lands die as a state-based action due to having zero or less toughness, as they are creatures due to Natural Affinity.
When the lands die, Massacre Wurm's second ability triggers for each land that dies this way, causing each opponent to lose 2 life for each land that died under their control.

Near-infinite lifeloss

Destroy all lands opponents control

Mass Land Denial

Massacre Wurm

Natural Affinity

Cast Natural Affinity by paying {2}{G}, causing all lands to become 2/2 creatures in addition to their other types.
Activate all mana-producing lands and/or creatures you control by tapping them, adding at least {3}{R}{R}.
Activate Aggravated Assault by paying {3}{R}{R}, untapping all creatures you control and causing you to get an additional combat and main phase after this one.
Repeat from step 2.
If lands and/or creatures you control can tap to produce at least {4}{R}{R}, this combo nets infinite mana.

Infinite combat phases

Infinite mana creatures you control can produce

Infinite mana lands you control can produce

Infinite untap of creatures you control

Infinite untap of lands you control

Aggravated Assault

Cast Natural Affinity by paying {2}{G} causing all lands into 2/2 creatures until end of turn.
Cast Act of Treason by paying {2}{R}, targeting Ink-Treader Nephilim.
Ink-Treader Nephilim triggers, copying Act of Treason for each creatures, gaining control of creatures until end of turn.
Cast Cloudshift by paying {W}, targeting Ink-Treader Nephilim.
Ink-Treader Nephilim triggers, copying Cloudshift for each creature.
The Cloudshift copies resolve, exiling all creatures you control and returning them to the battlefield under your control.

Gain control of all creatures and lands

Ink-Treader Nephilim

Act of Treason

Cloudshift

Animate the land that has Squirrel Nest attached using Natural Affinity.
Activate the land with Squirrel Nest attached by tapping it, creating a 1/1 Squirrel creature token.
When the Squirrel enters, Intruder Alarm triggers, untapping all creatures.
Repeat from step 2.

Infinite ETB

Infinite creature tokens

Infinite untap of creatures

Squirrel Nest

Intruder Alarm

Activate Marvin using Grove of the Burnwillows' second ability by tapping it, adding {R} or {G} and causing each opponent to lose 1 life due to Tainted Remedy.
Activate Marvin using Pili-Pala's ability by paying {2} and untapping it, adding {1}.
Repeat.

Infinite lifeloss

Grove of the Burnwillows

Pili-Pala

Marvin, Murderous Mimic

Tainted Remedy

Activate Arixmethes by tapping it, adding {G}{U}.
Activate Minamo's second ability by paying {U} and tapping it, untapping Ioreth of the Healing House.
Activate Ioreth of the Healing House's second ability by tapping it, untapping Minamo and Arixmethes.
Repeat.

Infinite green mana

Ioreth of the Healing House

Arixmethes, Slumbering Isle

Minamo, School at Water's Edge

Activate any number of creatures and/or lands you control by tapping them, adding at least {1}{G}.
Activate the land with Tarmogoyf Nest attached by paying {1}{G} and tapping it, creating a Tarmogoyf creature token.
When the Tarmogoyf enters the battlefield, Intruder Alarm triggers, untapping all creatures.
Repeat.

Tarmogoyf Nest

Combos with "Natural Affinity"