I made a video on how to summon Living Block pets in vanilla Minecraft. This is of course fake, but it shows one of many examples on how you can use this concept. 
https://www.youtube.com/watch?v=Lp6tubCAqt8&list=PL0tE7mOFabgJdg5dMZQXb_ILiSO0IncYW 

On one of my previous concepts I made block disguise possible in vanillia Minecraft. That version of the concept was very buggy, and the blocks did not look realistic.

In Block Disguise 2.0 I have made some changes! Now the blocks look like fully sized regular blocks. You are free to break and place blocks, and you can blend in with your surrondings 100%.

Do you like this concept? Leave a diamond to show your support!

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It is recommended that you watch the video before reading this. By using the 1.8 command /execute I have been able to upgrade my block disguise concept! If you are going to import this machine in to your world using MCEdit you might have to replace the redstone blocks the first time to give it a "kick start".

What is going on is that a command block is executing this command: /execute @a[score_disguise_min=1] ~ ~ ~ summon FallingSand ~ ~ ~ {TileID:2,Data:0,Time:0}
This command is summoning FallingSand entities looking like grass blocks. By setting Time:0 on the data the falling sand will not become solid and act as a ghost block. The moment a player moves from one place to another the ghost blocks will disappear. At the same time new ghost blocks are spawning on the player, making it look like a block disguise.

Since the blocks are ghost blocks this will not be solid, but you still easily hide while disguised. (I did it at the start of my video to show you how well it works).  

You can configure what kind of block you are disguised as by changing the TitleID. In order to disguise yourself simply type this command: /socreboard players set (player) disguise 1

To undisguise yourself type this command: /scoreboard players set (player) disguise 0

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Check out the first version of block disguise: http://www.planetminecraft.com/project/block-disguise-in-vanilla-3033811/