Playability is a broad category, and it is very subjective
Long story short Ragavan is a house against any deck, is pure mana acceleration and card advantage, and packs them both together in a body that should cost way, way more than one mana
What's not to like about an enchantment that can stop attackers, save your blockers, make your creatures invulnerable to removal, give you free morphing, and allow recursion of comes-into-play abilities -- for free
Emerge is a keyword ability that lets you cast a spell by paying its Emerge cost and sacrificing a creature rather than paying the spells normal mana cost
Let me know in the comments or over on Draftsims Twitter
The archetype was unprecedented and few other than Conley Woods and myself believed that the deck was real