My inspiration was the canvas game engine for the Valkyria Chronicles games.
This is a pure post-process shader made in Unreal Engine 4. It contains a custom screen border based on an image, as well as an image that gets drawn over every object in the world.
The result is a visual effect that suggests your world is hand-drawn, which gives an unique stylized appearance to your project.
Other features this shader has include:
Saturation control allows you to remove all the color in the scene, or amplify the color in the scene.
Outlines are drawn around every individual object, leading to a bit more visual seperation between them. Of course, the example given here is drastically exaggerated.
Color Grading allows you to quickly change the over color and feeling of your scene. There is a seperate color for the lines and for the overall scene.
The shader has been simplified to only contain essential features. With unreal, it is possible to layer post processing materials so there is no need to modify your existing shader, or this shader. In addition to that, it is possible to disable any unneeded features to further reduce the load of this shader. The total ammount of instructions without lightmap is 57. The vertex shader has 44 instructions.
I made this shader both in Unreal and Unity. The Unity shader lacks the outline feature, however.