Blizzard shared a picture on Twitter yesterday and the point was to find Valeera. The picture contains a lot of Heroes and infested terran eggs, pointing at the possible release of Alexei Stukov as one of the next Heroes.
We know for sure the next Hero won't be an Assassin. You can find the eggs near the bushes next to Zagara.
Here's how the eggs look like in Starcraft.
Have you found any other Hero you cannot identify?