Vree, I think that’s a rather good idea for a comic! The type of pony who’s always a day late and a bit short.
 
Pinkie moves to Ponyille to become a successful baker and wild-filly while Blinky moves to… Rockhaven… and becomes a low-income… bookkeeper and mild-filly? The kind of mare whose life is achingly dull and simple?

How about a comic about Blinky Pie: The Less Fortunate Sister where she follows in Pinkie Pie’s footsteps but everything happens differently/worse?
 
I’m thinking on the lines of:  
Pinkie Pie got her cutie mark in a sonic rainboom.  
Blinky Pie got her in a rainstorm that got her soaking wet.  
Pinkie Pie moved to ponyville and became an element of harmony.  
Blinky Pie opened a rock shop.  
Pinkie Pie eats so much sweets she’s a medical risk.  
Blinky Pie thinks a blade of grass on her dinner is a luxury.  
etc.  
etc.