The original version simply mapped a given domain to a randomly-chosen combination of Unicode 6.0 emojis (the ones that your original iPhone 4S supported) - nothing more. I was about to start sharing around the site when I came across http://www.xn--vi8hiv.ws (Linkmoji) and http://xn--cr8hhg.ws on Product Hunt - two great emoji URL shorteners that had already beaten me to the punch - doh!
After my ego finished deflating I began to think of ways to improve on the original concept. I assumed that the most-desired feature would be custom emoji combinations so I added that first (your custom alias can be between 1 and 100 emojis). I also noticed that emoji URLs don't play nice with social media - like, at all (Twitter being the only exception at the time of this post). Through a lot of manual testing I narrowed down the URL formats that would be supported (and autolinked) by all the major players (Product Hunt, Hacker News, Slack, Reddit, Twitter, Facebook, Pinterest, and Tumblr) and displayed them in a tabulated list upon shortening.
I also added detailed analytics. Originally I was just tracking clicks but ended up adding sources, mediums, cities, countries, browsers, platforms, and devices. Finally I added support for Unicode 6.1, 7.0, and 8.0 emojis which are what all modern phones offer - it currently supports 888 emojis (not intentional but awesome nonetheless).
All in all it took about three days to build the core functionality and another four to polish the User Experience (I'm a backend dev by trade so frontend work doesn't come as naturally to me). I'm sure there are many ways in which Mosho can be improved and I look forward to everyone's feedback! Finally I'm greatly thankful for http://www.xn--vi8hiv.ws and http://xn--cr8hhg.ws - their efforts inspired me to really push myself with this product - it wouldn't have been as polished had it not been for them.