Have you forced with issues in some levels in Delete One Part? Whole of ingame levels are very tricky to understand and finish.
So if you want to understand everything about this game and about all ingame levels you should get this application and read it.
In this application you find even Hints for secret levels in Delete One Part and you will be able to finish even those.
In app you'll find step by step videos and images for every DOP 2 level, and also little about hidden levels, which are very hard to get.
Enjoy