To get the Poley Skin, first you will need to play Chapter 10 – Mall and unlock the vault with the mirror. 
Unlock the Vault ! 
Now dodge the Lasers and reach the End. After you reach the End, you’ll hear a sound which indicates that you’ve gotten the Skin. 
Go to Skins tab and you will find Poley Skin there. 
Poley Skin Animation. 