When I did my mud edits I referred to pictures from the show of ponies covered in mud. Though when I did a similar one to this it was less popular than my other mud edits so I didn’t do that again.
 
Also what’s with the green to the left of Twilight?

I like it but yes its looks more like a puzzle.

Hmm, only advice I have is go a little more random in the “ooze” lines, they all look too simular with each other, sort of gives the image a “puzzle” look more than actual mud. I have also felt to less lines the better, of course it also helps with placement. Another thing is break up the outline a little, majority of the time mud is a rather lumpy in texture, so their outlines won’t be perfect, it’d be more broken up or lumpy.
 
Finally I’d work on putting in some highlights, mud is wet so there would be a lot of highlights and shine along the parts that are covered.
 
Hope this isn’t too confusing, I just got off work and am exhausted… Though I am no expert (trust me I am learning too) if you ever need any help or want a second pair of eyes to look over something, feel free and PM me, not enough messy artists around here.

This just reminds me that Everfree is likely not going to have any mud in it, despite them being at a summer camp- the opposite of paved roads and proper drainage. Oh well, nice enough.

@Rarity225
 
And yer gonna prepare the **“WHAT THE HELL SMUDGE PROOF!?”** tags.

@Alex Vostox  
I think I might just have to do that :p

@Rarity225
 
Yer gotta ask Smudge Proof fer that..

This is nice. Kinda disappointed at the lack of muddy Equestria girls pictures. Love it. :)

OP, you left some background on the eye of twilight and rarity also, Book Human’s left foot.

Cardboard board cut-out?