Board Thread:General Discussion/@comment-25860806-20150501225231/@comment-27159736-20150610213158

Gold seems to be the key phrase to Bill Cipher. When Stan and Dipper were confronting Robbie in Boyz Crazy, Stan told Robbie that the end of the world is comming and that he should bury his gold and in Dreamscraperers Bill told Gideon to buy gold.

This is can be either a reference to Samuel Pepys who buried his possessions during the great fire of london  or it means that Bill gets stronger by aquiring gold and the richest family in the town is bound to have gold somewhere so they could be his first priority/target.