A Very Serious, In-Depth Look at Pinkie’s Mane/Pinkie’s Cutie Mark Interactions
This is Pinkie Pie, and this is what Pinkie Pie’s mane looks like.
At least, this is what it usually looks like.
This is what Pinkie’s mane looked like from birth to the point she got her cutie mark.
This is what Pinkie’s mane looks like … not after she got her cutie mark, because she still doesn’t have it in this screen shot. But this is immediately before she gets her cutie mark, and it’s not long after Rainbow Dash’s first Sonic Rainboom and its resulting rainbow taught Pinkie how to feel joy.
This is what Pinkie’s mane looks like after she thinks her friends don’t like her anymore and want to kick her out of the friend group. It’s reverted to pre-cutie mark flatness. (Also, her mane and coat color have turned a somewhat darker color.)
This is what Pinkie’s mane looks like after Discord brainwashes her into thinking her friends are all laughing at her and not with her. It still remains poofy, though its color (and the color of her coat) have turned a bit gray.
This is what Pinkie’s mane looks like after Twilight accidentally swaps Pinkie’s cutie mark with Applejack’s. It’s flattened, much as it was pre-cutie mark, but unlike in “Party of One,” it hasn’t changed color.
This is what Pinkie’s mane looks like after Cheese Sandwich “steals” away the planning of Rainbow Dash’s birthday party. Neither its shape nor color has changed.
(Side note: Perhaps Pinkie is so upset about Rainbow’s birthday party at least in part because she wants to repay Rainbow Dash for what Rainbow did for her in “Party of One”? It’s a theory. *cough*RAINBOWPIE5EVA*cough*)
This is what Pinkie’s mane looks like after Starlight Glimmer steals her cutie mark. It’s still poofy but darker in color, much as it was after Discord’s brainwashing.
As can be seen from the above evidence, there is strong likelihood of a correlation between Pinkie’s mane and Pinkie’s cutie mark, but this correlation is clearly not a direct one-to-one causation. More research and analysis are required.