I made the tilesets. Some of the content of them was based on what Johnny requested to be in them, though the major concepts of the level design (e.g. the elevator shaft element) were my ideas.
Basically, whenever I get an idea for a KS level, I start making original tilesets, and I spend so long on them that I never get around to making the level itself. When Johnny was making Paradise Last and asked for collaborators, I saw an opportunity to rein myself in by making tilesets based on someone else's requests. But once I got started my ideas got ambitious (as always) and I ended up making tilesets so complicated that I had to do the level design as well!
So, aside from the originating idea for it to be set in an old abandoned building (which was Johnny's request), everything in the level is by me, with these minor exceptions:
-the intro screens which use screenshots from Paradise Last
-the creatures at the end which were made by Johnny.
-a few tiles on the very first screen (the street and streetlight) which were from Johnny's tileset for the Lost Vegas section of Paradise Last.
-level-design-wise, Johnny also did some minor tweaking of what I created.