Technically the one who invented the Emerald Dream was Knaak.
Knaak doesn’t mention the Titans in regards to the Emerald Dream but does say it is a Blueprint. The fact that it is the Pattern and extends across the Multiverse including the Cosmic Realms suggests that it is indeed a Blueprint though clearly one that isn’t fully used yet(probably because Nymue is forcing the Dream to not change which would lead to the Song to end and the finished Blueprint to be used).
Someone get Knaak to write stories concerning what the Emerald Dream truly is!