Intensity and motion lines (Backgrounds and overlays)

There are plenty of examples of this yet they go by many names; speed lines, overlays, motion lines and they have lots of uses too. I learnt that it was originally used to cut down on production costs as it was inefficient to create long scrolling backgrounds when something is moving fast. I can't observe this effect using first-hand sources (though it is based in reality as exaggerated motion blur), so I looked at some case studies:

I also isolated a frame and tried to redraw the background without the character:

Dead Cells animated trailer

Dead Cells: Rise of the Giant animated trailer 

Aggretsuko

I noticed that most of these had limited, looping animation, and a mixture of blurry backgrounds and moving lines.

It's usually used when there is a lot of fast, intense animation but it can be used to emphasise an object, or express surprise:

Dead Cells trailer emphasises the end castle using bouncy motion lines

Into the Spiderverse uses motion lines (paired with vivid backgrounds) to represent spider-sense

Since it's quite a straightforward, simple effect, I decided to do multiple Moom style tests:

I then did this:

What went well:

• Making Moom move slightly instead of being static meant that the intensity lines helped frame and emphasise the motion, instead of taking the attention away,
• Using a few flash frames with inverted colours made the toe stubbing more impactful.

What could be improved:

• The zigzag lines on the toe crack is slightly clunky, I should've looked at more case studies and examples,
• The motion lines on the corners of the toe crack blend in too much, I could've increased the contrast between the background and motion lines,
• The coloured background on the first test might be too jarring (since most of my tests have had a neutral grey background).