Startling megaphone I feel is very good in this deck. It get's rid of tools such as Fighting Fury Belt, Spirit Links, Bursting Balloons, and other annoying cards for this deck. It also helps against Garbodor being able to use your abilities for at least a turn.
I played Jimmy (the winner) with my Greninja deck, I lost 1-2 against him, the game I won I was able to set up and megaphone his garb, then nuke him down in 1 turn. With the popularity of the garb/darkrai deck at Origins, I think running 2 megaphone is a fine idea. There were also lots of metal decks and megaphones can help nicely against those being able to lysandre out a bronzong and go ham with the shurikins.
I probably could have down played into a tie, but I was already out of the running for a top 8 spot and didn't want to be a jerk.
Here was my lineup.
R1 - Manectric (1-0) Win
R2 - M Sceptile (1-1) Tie
R3 - Metal Gen+Bronzong+Aegislash (1-1) Tie
R4 - Night March (1-1) Tie
R5 - Darkrai Garb (1-2) Lose
I dropped after this point
I had tons of ties, I didn't get to practice this deck online as much as I wanted because I can't get those Jirachi's.