Cyrus Gold is the civilian name of a popular DC villain, Solomon Grundy.
Near the end of the episode, Diggle asks Oliver about Cyrus Gold's whereabouts, to which Oliver responds "Died on Saturday, buried on Sunday." This alludes to the "Tale of Solomon Grundy," whose real name was Cyrus Gold before he died.
During the news broadcast that Barry Allen watches, the reporter notes that her name is Linda Park. Linda would later be recast with Melise Jow and play a love interest for Barry in Season 1 of The Flash (2014).
This is the episode where Oliver receives his compressible micro fabric mask, custom made by Barry Allen, after Barry points out that grease paint is a poor identity concealer. Oliver's criteria for a mask was one that conforms perfectly to his face and doesn't affect his ability to aim while on the run.
The three ghosts in this Christmas episode are a reference to the three ghosts in the famous Charles Dickens story, "A Christmas Carol".