I was curious as to why Slaughterhouse is not a required level when it's part of the original levels.

I have no idea... :/ But rules are rules, right?

I honestly think these categories need some revision. Slaughterhouse not being included when it's an original map plus people on PS3 don't have access to No Mercy so there would need to be a new DLC category for that.

I plan on running the co-op No DLC run but the addition of Slaughterhouse means another level that needs to be optimised compared to the solo run. It either needs to change so the solo run also has to do Slaughterhouse or at least remove it from the co-op run.