I agree with Innovator. If your talking about the mandarin, they need a large established tank with lots of live rock to survive because they only eat live foods; however, some have been able to eat prepared foods, but these are hard to come by.
Same thing goes for the Spotted Green Mandarins and Scooter blennies.
One thing I noticed when I was at my lfs was they are so cheap. They were under $15, pretty much the cheapest sw fish you could buy but one of the harder ones to keep. And most of the people that buy them dont have the proper accommodations for one.