Purchasing a Pro subscription will give you masking tools via the Influence Panel in the Mac/PC app. Pixlr for Desktop does not contain layers or other tools that you might be familiar with in Pixlr Editor.
Pixlr for Desktop is designed for photo editing. It's not the same kind of graphic design tool that Pixlr Editor is, so you may want to to use Pixlr Editor if you need to do graphic design work.
We don't offer a downloadable version of Pixlr Editor. Check this article out to see the visual differences between the apps.
Here's a detailed breakdown of some of the differences in our apps.