You can only get moshlings one at a time. You can get a set of moshlings by attracting one moshling, then attract the next one, until you have the set of all four moshlings.
You can not sell Moshlings on Moshi Monsters. When you first get a moshling you can choose to keep it or set it free.
So far, each set of Moshlings has four Moshlings in it. Since the Secrets set already has four Moshlings, it is unlikely that Moshi Monsters will release any more Secret Moshlings.
There is no set of moshlings on Moshi Monsters that is called "Sassy".
Each set of Moshlings on Moshi Monsters has four Moshlings. The set of Tunies Moshlings contains Wallop, Plinky, ^Oompah, ^HipHop Oompah and HipHop have not been released as of October 2012.
There is no secret monster on Moshi Monsters. There is a set of Moshlings called the Secrets.
The set of four Secret Moshlings on Moshi Monsters are Roxy, Lady Goo Goo, Blingo and Dustbin Beaver.
There are actually 4 moshlings in the Secrets set on Moshi Monsters. Secrets: Dustbin Beaver, Blingo, Lady GooGoo, Roxy
Reptiles as a specific set have not been on Moshi Monsters, however, several moshlings could be considered reptiles such as Snookums and Shelby.
DJ Quack the moshling is in the Birdies Set of moshlings on Moshi Monsters
Nothing you just have a full set of moshilings.
You can not delete moshlings on Moshi Monsters. If you are a free Basic Member, you can choose "Set It Free" when you get a new moshling, but the moshling that you set free goes to your Moshling Zoo in case you ever get a paid Moshi Monsters account. If you are a paid Moshi Member, moshlings go to your Moshling Zoo.
You can not swap moshlings on Moshi Monsters. When you first attract a moshling to your Moshling Garden, you can choose to 'Keep It' or 'Set It Free', after that, if you choose to 'Keep It", the moshling stays in your Moshling Zoo.