Sideboarded in Rakdos Shred-Freak for Grudge Keeper, after going 2-0 in Rd. 2, when I realized no opponent would ever vote to trigger the Grudge. Sideboarded in Nyx Infusion, Armament of Nyx, Arrest, and Vow of Duty for Sightless Ghoul, Guardian Zendikon, and Rakdos Shred-Freak after going 1-1 in Rd. 3, when I realized how vulnerable deck was to Flying, intending all four to be suppressors of opponent's creatures.
Before Rd. 4, removed Nyx Infusion, since -2/-2 is often not takeout on the creatures I need to suppress, and to return to a 40-card deck since I am still at 17 land, and had had to mulligan once in Rd. 3.