This...is amazing. You know, I think you've solved the problem regarding a Pony's mane and tail. Some artists use yarn, some cloth, some artificial hair...but it often doesn't look quite right. But the mane and tail on Mac is perfect. I think what you've done for Mac would work on a Derpy as well. Congrats, this plush is amazing!
The differences are subtle but I think more noticeable in person. Aside from having a longer mane, the eBay one is leaner than I'd like big strong Mac to look and his eyes and cutie mark are directly painted on (rather than made separately and inset as in this one). A technique I won't stick with cause some of the paint crackled.