Basically this is me summarizing these articles. Read them yourselves if you want the full story.
- The mantid worship an Old God named Y'Shaarj (so there is more than the just the three, C'thun, Yogg-Saron, and N'zoth).
- He apparently has seven heads, so you can speculate that the box of Yogg-Saron may be referring to him.
- He was killed by the Titans, which doesn't make sense to me since I thought if the Old Gods were killed then Azeroth dies... (he is CONFIRMED dead by the way)
- His essences is the Sha, which he let loose before dying
Original Well of Eternity (THIS IS SPECULATION & THEORIES)
- Throughout Pandaria quest lines it is referenced that the waters and rivers have magical properties
- Mogu, like the Elves, evolved from the waters in the Vale of Eternal Blossoms
- Before the Sundering, the Pandaren were in traveling distance to deliver a gift to the kaldorei, indicating that Pandaria and the Well were close to one another
- The water in The Terrance of Endless Springs has the same shimmering and pulses quietly like the water under Nordrassil does
- Jinyu also originated from those waters
What I'm saying is... the water in Pandaria is the remnants of the Well of Eternity!
Not a remake of the Well like Illidan made or one created by killing a Naaru, but THE ORIGINAL. This explains the mists, it shrouded the island protecting its waters from the world (the remaining Highborne and the Burning Legion).
If this is true, and now that the mists is gone, what does this mean for the future of Azeroth?