Some suggestions to consider: take out Manalith, Opaline Unicorn, Embodiment of Spring, and Gruul Keyrune, replace with Gruul Signet, Simic Signet, and Izzet Signet, and Sol Ring. For flying, Wonder provides a similar effect to Archetype of Imagination, and is a little harder to deal with. You will want to add more lands to this deck in order to cast your big creatures on time. I would say 35-38 lands, and cut some of your sorceries for ramp spells like Rampant Growth, Farseek,Cultivate, Kodama's Reach, Explosive Vegetation, or Skyshroud Claim. Thassa, God of the Sea is a more reliable way to make creatures unblockable than Invisibility or Way of the Thief. I always include a copy of Decimate in any deck that can play it. The same goes for Cyclonic Rift and Chaos Warp. Lastly, a few creatures that you could upgrade your deck with: Sakura-Tribe Elder, Joraga Treespeaker, Sylvan Caryatid, Courser of Kruphix, Genesis, Avenger of Zendikar, Prime Speaker Zegana, and Progenitor Mimic.