1. Draw the design using the vector tool.  
2. Convert it to a marquee (Feather at 1 adds a bit of blur around the edges so it’s not such a rough shape)  
3. Fill tool at slightly less than 100% opacity (to preserve the “texture” beneath)  
   Like this:  
   
    
   You’d have to play around with it a bit to get it right, but give that a try. You’ll be able to make it look good.  
   (I used this pic of yours; hope you don’t mind)

History lesson!

So there’s this dude DTK here on the site who takes screenshots and edits them to be quirky, silly, or downright terrifying depending on what mood he’s in. He also makes some nice spoiler pictures for the site. Whole gallery is here.

One fine day, he made this and came up with this ridonkulous description about them describing them as if they were a pet. And the concept just appealed to a lot of us artists. Me, Keith, and Heir-Of-Rick to name a few all pounced on the idea with Heir-Of-Rick even including Tatzljack as part of his Miss Pie’s Monsters blog.

So far the more or less universal consensus on what they are and how they act, since DTK didn’t think it would become a thing and thus never really gave it any thought beyond that one picture and basically just embraced what everyone else did with it, is that they swallow loved ones to carry in their stomach (or crop) which is designed specifically for this purpose (no digestion or suffocation), and that they’re otherwise basically just a normal pony with the eye markings, tongues, and tail of a tatzlwurm. Some artists give the species the split jaw and spines on the tail, others forego the split jaw and have fur up the tail or just at the tip, all of which is just preferences of course. My personal headcanon is that they’re very motherly and protective of loved ones, but since their means of doing this is down the hatch it can cause some problems or misunderstandings from those who aren’t expecting it, and that Tatzljack is her own separate entity from Applejack, and sometimes they even exist side-by-side (I draw her hair down and messy when that’s the case).