Ok. So recently I uploaded a dragon spawner. I did say in the additional information that I might do a tutorial. So I am. I will be using MCedit for this, so download it here. I will also be using some of sethblings custom filters, download them here. These are the steps to create a custom spawner (There are a lot more than just sheep and pigs etc. There are also things like, fireworks, tnt, sand and firecharges).

1. This is probably the most boring part. Making a new world and deciding which thing your going to make a spawner out of. So make a new world and find your mob.

2. Then exit out of minecraft and go into MCedit. Select your mob. This is probably pretty self explanatory (Note: leave a bit of space, as the filter were going to be using is 1 or 2 blocks off).

3. Go into the filters tab and select create spawners (You might have to download this depending on which version you are using). Tick Include Position Data, then click filter.

4. BAM! You should have created your spawner! If it is not there then try again with a bit more space. Now just move it somewhere or save it to a schematic.

5. Happy mob farming!