Cipher Twins and Bill.
 Do not summon them at all costs.
Background found here: http://img2.wikia.nocookie.net/__cb20120629194748/gravityfalls/images/0/04/Gravity_Falls_Opening_Ending.PNG
The file was too large, so I had to cut out a few frames. >.< The more completed version can be found here: http://veynn.deviantart.com/art/Cipher-Twins-449016840

Cipher Twins and Bill.

 Do not summon them at all costs.

Background found here: http://img2.wikia.nocookie.net/__cb20120629194748/gravityfalls/images/0/04/Gravity_Falls_Opening_Ending.PNG

The file was too large, so I had to cut out a few frames. >.< The more completed version can be found here: http://veynn.deviantart.com/art/Cipher-Twins-449016840