Did you guess it
Polymorph decks have an inherent weakness that if they draw their key creatures, they often cant cast them, and they no longer have their important targets in the deck for something like Creativity
Graven Cairns, for instance, was just re-released in Duskmourn, while Flooded Grove has been printed into the ground, with recent appearances in Thunder Junction, Bloomburrow, Duskmourn, and Tarkir: Dragonstorm
The last is the nasty one that puts this deck over the top as a life-gain trigger for combos that you can never stop
(Artifacts, legendaries, and Sagas are historic.) Legendary Creature - Peasant Halfling Saradoc, Master of Buckland Whenever Saradoc or another nontoken creature you control with power 2 or less enters, create a 1/1 white Halfling creature token
Archetypes like Devoted Druid combo or Heliod, Sun-Crowned combo often make use of Ranger-Captain of Eos for a few reasons