Angel's Grace Celestine Reef Cloudsteel Kirin Courageous Resolve Gideon of the Trials Herald of Eternal Dawn Lich's Mastery Liliana's Other Contract (double-faced)(playtest) Platinum Angel Platinum Angel Avatar The Book of Exalted Deeds
Considering that both cards are in print and, discounting the Aftermath debacle, is from Magic's newest set, I'd lean towards selling while prices are high unless you plan on building the deck yourself
While some hyper efficient, single-target interaction like countermagic and Path to Exile is useful, you should also invest in cards like Grasp of Fate, Soul Shatter, and Convert to Slime to keep ahead on cards while putting your opponents behind on the board
They also seem to have released other product preorders for more future sets such as for Avatar The Last Airbender, Lorwyn Eclipsed, and Secrets of Strixhanen.
doing the best with what you've got
We'll want to run the usual suspects like Rampant Growth, Kodama's Reach, Explosive Vegetation, and the decision of whether or not to run mana rocks will probably be a meta call
