I just love all the supernatural types of sims that come with the Supernatural Expansion pack, but it makes the other towns seem boring by comparison. What we're gonna do is spice things up for a non-magical town!
-Make sure you have the options set that Supernatural sims won't spontaneously generate in your town. Also, choose a town that doesn't have a native supernatural population (Basically any town except Bridgeport or moonlight falls) ghosts don't count for this challenge.
-Also make sure the town doesn't have an alchemy store, supernatural hangout or any of the supernatural rabbit holes. You'll be adding them later.
-Create a family of supernatural sims. You need at least one person to be an alchemy master (I recommend a witch sim for this) but the other family members, if you make them, can be whatever supernatural and do whatever they want in town. Set the family down onto a lot and get to work!
The game proper:
-Buy an alchemy station for your alchemy master and set them to work making potions of all kinds. You're going to aim for the potions that transform sims into supernatural types, but those don't start showing up until later levels.
-If you have a sim who is a werewolf or vampire, have them start making friends so they can "infect" their friends with their supernatural condition. But make sure to ask nicely first!
-Back to the alchemy master. When this sim has a steady supply of supernatural-causing potions, have them make friends around town and upping the population of supernatural sims with their potions!
-Once you've got some money in the bank, buy a community lot and place an alchemy store. You can also place the Arborterium, the Gypsy wagon, and the Vault of antiquity. With even more cash, you may want to place a supernatural hangout!
-The challenge is complete when the ENTIRE population of this town is some sort of supernatural. Now your magic sims aren't so lonely anymore! But do try to balance the populations of supernatural types. If you've got a town that's entirely vampires, they won't have anyone to drink from! Don't be afraid of adding types that aren't in CAS either, Variety is the spice of life!