Haven't seen Mattoon mentioned in any Pizzagate research before. Surprisingly, there is not very much information about Dan Mattoon or Daniel J Mattoon on the internet from any search engine.

"Podesta notes that he and Mattoon have "a great old mutual friend" -- House Speaker J. Dennis Hastert, whom Podesta has known since college days. Mattoon ran Hastert's first congressional campaign. - https://www.washingtonpost.com/archive/politics/2001/01/25/veteran-republican-joins-podestacom/ffe75dd1-9be1-4cf1-bdde-b027439011f5/

Hastert Inc article from 2005 - http://articles.chicagotribune.com/2005-05-29/news/0505290316_1_dennis-hastert-jack-abramoff-delay/3

Hastert's son hired by Podesta/Mattoon: As a lobbyist, Hastert worked on, among other specialties, technology issues. Piggybacking on that, his older son, Joshua, hit Washington soon after Denny became Speaker in 1999. Voila! The pierced-tongued owner of a record store in DeKalb called Seven Dead Arson became a lobbyist focusing on technology and defense issues. Josh started his new gig, working for mp3.com’s lobbyist who had been an aide to former House Republican Minority Leader Bob Michel, a close colleague of Josh’s father.

Josh then moved to a small firm, Federal Legislative Associates, that lobbied on tech issues. Moving on up, he was soon hired by lobbying firm, Podesta Mattoon, headed by two old friends of his father’s—Tony Podesta, a fellow Illinoisan, and, with Hastert, a student government leader in the 1960s, and Dan Matoon, a close friend/advisor of Hastert’s who ran his first congressional campaign. In 2006, while his father was still holding the Speaker’s gavel, Josh was hired by Google as part of a team of Podesta Matton lobbyists. - http://www.chicagomag.com/Chicago-Magazine/Felsenthal-Files/June-2015/Dennis-Hastert/