Seasons Gnomes.
♦ Cracklin Nakerbell (Fall) – This gnome can be found after a night of Trick or Treating, or a scary survival in the Haunted House. They also spawn on lots that have a Scarecrow.
♦ Bucktooth Butternut (Spring) – This gnome is found on a residential or commercial lot that has a beautiful garden arrangement, and even on a lot that spawns wildflowers. They also spawn during Egg Hunts.
♦ s-GNOME-man Bittertotter (Winter) – When you build a snowman on your home lot or in the park, chances are this little guy appears. There is also a good chance of him showing up on Snow Days when the town is buried in snow!
♦ Brawn Brawn G’nome (Summer) – Wherever there are Fireworks, Barbecue’s & Pool Parties is where this gnome loves to be. Party on!
♦ Evil Gnome (Year-round) – Ever explore the catacombs and come out with a regular happy gnome? Well now there is a chance you will come out with the Evil Gnome! These little mischievous creatures can cause havoc in your home and disrupt your beauty sleep. They will un-set your bed, kick down your trash, and even give you a Gnitemare! Be aware of your surroundings when you sleep! (The chances of you finding this gnome increases when you have enemies, or carry the Evil trait).
Source:
http://simsvip.com/game-guides/sims-3-seasons/ I got the Evil Gnome while Trick or Treating.