These Horizons sets, historically, have affected the Modern format so severely that they undergo a pseudo-rotation. Basically, the format looks entirely different at its most competitive level after their release
So it's understandable that infinite mana is incredibly powerful, especially in Commander
(If it would be dealt damage or destroyed, remove a shield counter from it instead.) If an Aura is put onto the battlefield without being cast, the Aura's controller-to-be chooses what it will enchant as it comes back onto the battlefield
In hindsight, we should have named it something different, like mana identity
Summary Bloomburrow introduces enchantments that look like Sagas but are more permanent, influencing Magic's meta in a new way
As Bonus Cards go, this one if a bit of a slam-dunk