Springbloom Druid | Springheart Nantuko

Cards

All permanents on the battlefield (
Springheart Nantuko attached to
Springbloom Druid).

Play a land.
When the land enters,
Springheart Nantuko triggers, causing you to pay ({1} magic symbol) ({G} magic symbol) to create a token copy of
Springbloom Druid.
When the
Springbloom Druid token enters, it triggers, causing you to sacrifice a land, then search your library for a basic Forest and another basic land and put them onto the battlefield tapped.
When the Forest and other basic land enter,
Tiller Engine and
Springheart Nantuko trigger twice.
Resolve both
Tiller Engine triggers, untapping the basic lands.
Holding priority, activate both lands by tapping them, adding ({1} magic symbol) ({G} magic symbol) .
Resolve the first
Springheart Nantuko trigger, choosing not to pay and creating a 1/1 Insect creature token.
Resolve the second
Springheart Nantuko trigger, causing you to pay ({1} magic symbol) ({G} magic symbol) to create a token copy of
Springbloom Druid.
Repeat from step 3 until your library contains no basic lands.

You can perform this combo if half the basic lands in your library aren't Forests, but you won't be able to grab all basic lands unless you supplement ({G} magic symbol) to compensate. While you will put all basic lands onto the battlefield, you'll have to sacrifice half of them to continue the combo. This won't affect how many landfall triggers, ETB triggers and creature tokens you get however.

This combo has been estimated to be Exhibition (Bracket 1+).