The Smiley Moon has actually existed for quite some time. Now it exists as a written pattern too. Find it at Ravelry or as a package with 3 amigurumi patterns at LoveCrafts.
To celebrate the 1st anniversary of StoneGnome, the next pattern will be FREE for a couple of days. It should be released later this week. (Jfyi, it is not the heart shown here).
I like a method, where both yarn ends are easy to hide afterwards. Here is a tutorial of how to do that.
Some DIY pages have omitted a few details about splitting yarn. I've added these points to this guide.
Get links and patterns here.
I'm sharing my preferred methods for each of the basic slip stitch types with you. They are almost invisible on both sides of the work.