Enter "RXYMCPENCJ" as a code to unlock the Dr. Aiden Krone skin in Multiplayer mode. -From: vitruvian_soulless
In the battle with Dr. Krone's gigantic Sentinel, when you destroy one of his guns with the Pulse Gun, Krone will send artillery raining on your roof. In order to escape this barrage, slow time, and go into the far right corner. Face the wall and look up at Krone's Sentinel. Jump up on the platform. Keep running to the right into the corner. You will take no damage while in that corner. This works for all three barrages.