Retreat your active Pokmon by discarding energy from it equal to its Retreat Cost, and replace it with a benched Pokmon
Originally printed in 2012s Return to Ravnica set, Trostani costs two green and two white mana for a 2/5 legendary dryad
While this may have been partly because a Modern Pro Tour was around the corner (Birthing Pod, which we'll talk about in a minute, was banned at the same time), there were few complaints from the community because unlike other Pro Tour-related bannings, it was clear to pretty much everyone involved that the cards were simply too efficient for Modern
If youve ever stared down a Storm deck with a free-mana engine, you know exactly how dangerous this kind of effect can be
[7] So, if youve got a Goblin Guide on the field and then you play an Eidolon of the Great Revel, the devotion count is 1 when the Eidolon is on the stack, but 3 the exact moment the Eidolon enters the battlefield