I did a little lurking around on this forum, and I agree primarily with Earthworm in terms of direction. Picking a type that has poor offensive coverage and compensating by giving it great stats and movepool doesn't teach us anything or give us anything creative to work with. While necturna was a fantastic CAP, it did seem to be a standard bulky attacker that happened to be able to use sketch and was balenced as not to be broken. I'm not really sure that fit the concept very well, as Necturna doesn't rely on her sketch flexibility so much as her shear statitisical bulk. Anything, and I mean almost anything, could be OU if we added enough to its movepool and stats. What we should be focusing on accomplishing here is a pokemon who's typing isn't extremely well suited to the task at hand, but doesn't have to rely on a standard bulky attacking spread with a fantastic movepool to compensate. The typing, in my opinion, shouldn't be the worst type we can find, but rather the one that makes the most interesting pokemon.
Finally, I'd like to pose a question: Which type/type combination is most unlikely to be seen as defensive/offensive, and how can we make it work without a heavy reliance on an overcharged stat and move pool?
It may seem stupid, but I'd like to see a pokemon whose type, while strange, is good enough that it can stand with a fair movepool and reasonable stats.