Cast Life by paying {G}.
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 Life
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

Massacre Wurm

Life // Death

Cast Life by paying {G}, causing all lands you control to become 1/1 creatures that are still lands until end of turn.
Activate all mana producing lands and creatures you control by tapping them, adding at least {4}{R}{R}.
Activate Aggravated Assault by paying {3}{R}{R}, untapping all creatures you control and getting an additional combat and main phase after this phase.
Repeat from step 2.

Infinite combat phases

Infinite mana creatures you control can produce

Infinite mana lands you control can produce

Aggravated Assault

Animate a Forest that enters untapped using Life // Death
Cast Springheart Nantuko for its bestow cost by paying {1}{G}, attaching it to the animated Forest.
Play a land. When the land enters, Springheart Nantuko triggers, causing you to pay {1}{G} to create two token copies of the Forest that enters untapped.
When the Forest tokens enter, Springheart Nantuko triggers twice.
Holding priority, activate the Forest tokens by tapping them, adding {G}{G}.
Resolve the first Springheart Nantuko trigger, choosing not to pay and creating two 1/1 Insect creature tokens.
Resolve the second Springheart Nantuko trigger, causing you to pay {1}{G} to create two token copies of the Forest that enters untapped.
Repeat from step 4.

Infinite ETB

Infinite creature tokens

Infinite landfall triggers

Infinite tapped Forest tokens

Springheart Nantuko

Doubling Season

Cast Life by paying {G}, causing all lands you control to become creatures until end of turn.
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 from step 2.

Infinite lifeloss

Grove of the Burnwillows

Pili-Pala

Marvin, Murderous Mimic

Tainted Remedy

Cast Life by paying {G}, causing lands you control to become a creature until end of turn.
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 from step 2.

Infinite untap of lands you control

Infinite untap of all creatures

Tarmogoyf Nest

Intruder Alarm

Animate the land that has Squirrel Nest attached using Life
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.

Squirrel Nest

Cast Life by paying {G}, causing all lands you control to become 1/1 creatures that are still lands until end of turn.
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 from step 2.

Infinite green mana

Ioreth of the Healing House

Arixmethes, Slumbering Isle

Minamo, School at Water's Edge

Combos with "Life // Death"