Here is how to unlock all the skins in Granny Simulator version 0.0.7
Ninja skin: Make sure you KILL granny with a kunai on the Halloween level.
Creepy Doll skin: Make sure granny has no cookies on the tray when she goes to the demon.
Ventriloquist Doll skin: Make sure the house burns down. In order for the house to burn down you must not let granny take the cookies out of the oven.
Pumpkin Head skin: Make sure granny wins the Halloween level. (Can be made on single player and as you lose as a toddler, you get the granny skin for some reason).