I noticed that this category isn’t closed. The only shop item I could think of that you can use for this level is wall-nut regeneration, but slot machine also uses that and that shopless category is closed. Is there something I’m missing?

The other thing that can be used in Portal Combat is the Rake, though given that the normal strategy also doesn't use the Rake the Shopless category for Portal Combat should probably be closed as well. I'll go do that now.