They are equally rare. I have gotten 4 drill demons and 10 mimes, but mimes have been out much, much longer. Since drill demon came out, 2 mimes and the 4 drill demons. As for how to get a mime, you'll just have to wait and hope you get it.
Stick to a skill for a long period of time and you should get plenty of randoms. They are random, yes, but are also meant to stop autoers who generally do 1 skill, and 1 skill alone.
The window closed on me once... I didn't tell it to, but it did... Lost 970,000 coins and some raw lobsters... Oh, and my lobster cage :cry: 100th post :thumbsup: \