Again, go to Filter > Liquify, and using a Bloat Tool, click a few times on its face to to make it look more bulbous.
It's the right time to add some brushes. We need 3 brush sets to complete this illustration. I use these 3: Feather brushes, Ink Splatter, and Cracks brush for the wall. Grab a Brush Tool and start load our brushes. Use the [ key to decrease the brush diameter. Rotate and put it in various places to see what it looks like in different positions. Make sure you use each brush on its own separate layer, that way you can move each layer around to line them up, and play with their Opacities.
To create a mouse hole in the wall, just add a new layer above the Pattern layer and draw kind of an oval shape using a Brush Tool with 100% Hardness. You can reshape it using an Eraser Tool, so it doesn't need to be perfect. Go to Layers Panel and add an Outer Glow Layer Style with the settings as shown in the image below.
OK, we're now going to start adding some drawn elements. Open some of the elements you want to add to our canvas, and Press Ctrl+I to invert the color. Put them above the Wall group, set the Blending Mode to Screen and lower the Opacity down.
Now we're reaching the final of this tutorial. As for the final touch, flatten all the layers down and go on the top of Layers Panel and add a Color Balance and Levels adjustment layers with the settings as shown below. This will unify the illustration and blend the color together.
Refer to step 6 to create a vignette effect to focus the attention on the center of the image. Now duplicate the layer, press Ctrl+U to desaturate the color, then go to Image > Adjustment > Shadow/Highlight and leave the settings as it is. Set the Blending Mode to Soft Light and the Opacity to 30%.
Next, to add a bit of contrast and keep the edge details, just duplicate the layer again, go to Filter > Other > High Pass and set the Radius to 3.0. Then set the Blending Mode to Overlay with the 30% Opacity.
Lastly, add a Hue/Saturation Adjustment Layer on top of everything, and set the Saturation to +5.