It's inevitable that when a great game is created, there will be others that try to duplicate its success, sometimes right down to the look and feel. Pocket Devil is almost a direct copy of the very popular casual game Pocket God. The app takes the formula of having different victims and giving them plenty of ways to interact or die from their environment. This particular app focuses on demons and the different ways you can torture them.
Players have the ability to do various evil things such as hang them from chains or decapitate them using a guillotine. The game is set up in such a way that it will be updated with different chapters just like Pocket God.
The thing to note here is that it is not created by the same company. Using the same idea is nothing new to the app store and I personally see nothing wrong with it. But the quality of this particular game is definitely lower when compared to the much more advanced Pocket God.
It is currently free in the app store, but I suggest looking into Pocket God. It has a ton more things to do and is frankly just way more fun to play around with. This game just feels like a Halloween version of the app that went slightly wrong. But the developers may keep improving and adding more to it so keep an eye out for updates.