Secret mini boss

The idea would be mini bosses get added to the game but go unannounced. Nobody knows they exist. They would be summoned like the wither, snow golem, and iron golem; that is, a specific selection of blocks in a specific shape. Essentially it would be a countdown until someone discovers it and posts about it then a flood of people would be taking the challenge to fight it, posting videos and fan art online, etc. 

beyond that is an open book that Mojang could take any direction. Make it a seasonal thing and/or remove it all together, keep it in, add new hidden bosses? I think it would create a lot of traction in the Minecraft fanbase much like the elusive Herobrine did, a sense of mystery perhaps?