Springheart Nantuko | Mutable Explorer | Horizon Explorer (and one other card)

Cards

All permanents on the battlefield (
Springheart Nantuko attached to
Mutable Explorer).

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
Mutable Explorer.
When the
Mutable Explorer token enters, it triggers, creating a Mutavault land token that enters untapped due to
Horizon Explorer.
When the Mutavault token enters,
Springheart Nantuko and
Nissa trigger.
Holding priority, activate the Mutavault token by tapping it, adding ({C} magic symbol) .
Resolve the
Nissa trigger, adding ({G} magic symbol) .
Resolve the
Springheart Nantuko trigger, causing you to pay ({1} magic symbol) ({G} magic symbol) to create a token copy of
Mutable Explorer.
Repeat from step 3.

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