Why can't we just spawn a EntityPlayer with the name of Herobrine. The client will be told that there is a player called "Herobrine" here. The skin for account "Herobrine" will be downloaded from minecraft.net by the client. Oviously, if the skin for account herobrine changes, the plugin will break. The plugin can be coded to tell the EntityPlayer what to do, such as place blocks, swing arms, look at player. Perhaps we could use the movement coding of a enderman? We can maake the plugin reconnise a configurable altar being build, and spawn a EntityPlayer nearby. I am sure this is possible to make a plugin like this without SpoutCraft server or clientside.