Hey, how can I do that an NPC is moving its head to a client, so every player on the server sees the NPC looking to him, how do I place blocks on special clients, blocks that only the speacial client sees.
You can, look on BrokenLens how the NPCs look at you or on LBSG where blocks are spawning when you are going to buy a kit
I can see how you could code an NPC that looks at the nearest player, not how you'd allow every player to see it looking at them though unless it was done somehow in the PM core. And making blocks spawn when you buy a kit isn't the same as each client seeing different blocks...
I'm not really sure what specifically you're asking for. If you want everyone on the server to make it look like a mob is looking at them, you need to send individual entity move packets to everyone. I don't have much examples but this is something that would be relatively difficult to implement - you'll have to look into how PocketMine manages viewers to accomplish such a thing. Same thing for blocks only appearing on specific clients, you need to send block update packets to individual clients.
You can always create your own NPC Class that features movement and packet handling, make your own methods inside the class and the result will end in Packet Handling
You can't !== it's impossible... To be more precise, until one of the Dev team decide it's worth implementing, or you learn advanced packet handling and build your own version of pocketmine, you can't xD
Not really, anybody can make a plugin with custom classes and just redirect the actions from their Custom Entity to an existing Entity event, or even better, create a custom event. See also: EssentialsPE Events
That's very interesting, but too advanced for me for the moment. I'd hope anyone who is able to do that tries to fix the core teleport() glitch first though