Ok regardless of whether or not he finds a frozen eating mandarin this is a 12 gallon tank and it would need to be fed at least twice a day, they are slow eaters and miss tons of food, are you going to recommend this to someone new to the hobby? This is a job for someone dedicated to water changes and feeding, plus very few will take frozen anyways. Scooter blennies are more likely but still not a beginner fish. A 12 gallon is a small tank, a occ. clown would be a good choice, clown goby, maybe a blenny or royal gramma. No angelfish is going to be able to live in that tank, they are an active fish that picks off life on the rocks and need an established tank, putting a large angel in there would be a death sentence. I have a 12 gallon and had a yellow clown goby and tailspot blenny. Both good choices for a small tank. If you want big fish you are going to have to set up a larger tank as 12 gallons are only really good for small perchers or bottom dwelling fish like gobies/