Minecraft CreepyPasta Wiki talk:Herobrine and Entity303: The Truth Revealed/@comment-9770324-20150302165651

/summon Entity303

is nothing more than another Mojang prank (after the upside-down Dinnerbone & Grumman mobs), which spawns a skull with owner name Herobrine and makes plenty of explosions and nothing else (though it says "Unknown command").