In the mission where you will fight Nero, you will collect 4 items. By doing that you must collect so many cardkeys. One of the items has many laser walls. One cardkeys are hidden behind the shop. Another is in a cargo in the tunnels. One again in a explosive barrel, you can see it clearly when you are in the building where the Deepground gatling guns are. its on a left building. another is where you go in a tunnel, Vincent will say "Up there???."

Now look upwards beside the lights, shoot the hanging mine and it will drop a cardkey. last one is where you will fight nero, dont go any closer on that area, it is only on the end of the cliff, so be careful or you might drop and cannot get back again to finish the mission. if you get a first cardkey go and get the cardkey open the laser walls where it has 2 cardkeys only, second open the one that has many walls, you will get the lucky barrel, second open the one that is beside the gatling and you will get the bayonet, then open the one beside the vents last, because it will only give you a limit breaker, the other one is in the other side of the broken pipeline.

Submitted by Suicune17 (Perpectagon)