Nim Deathmantle + Llanowar Druid + Concordant Crossroads
Nim Deathmantle
Llanowar Druid
Concordant Crossroads
Infinite death triggersInfinite creature ETBInfinite green manaInfinite creature LTBInfinite creature sacrifice triggersInfinite untap of Forests you control
How it works
Activate five Forests by tapping them, adding .
Activate Llanowar Druid by tapping and sacrificing it.
Llanowar Druid dies, triggering Nim Deathmantle, causing you to pay 4 to return Llanowar Druid from your graveyard to the battlefield, and attach Nim Deathmantle to it.
Resolve the Llanowar Druid ability from step 2, untapping all Forests.