I've absorbed all the posts here and I've come to a personal conclusion...
@Dusk: A Gear Shift or even a Coil set isn't going to work unless we give this guy some serious coverage, and even then it'll probably be outclassed by somethign like Sd Virizion (I'm thinking you're have to give it something ridiculous like Fire Punch or Close Combat). It's STABs are just too poor for a clean sweep in OU, and it's even going to have trouble wallbreaking with all those steels hanging around (even Jirachi and Bronzong are huge problems what with the terrible selection of physical Ghost moves available). There's even a bunch of common pokes that actually outright resist Grass and Ghost without even being Steel. Honestly, it's safe to give this guy good PS, and we're doing it a disservice if we don't. Also, when it comes to nerfing one offense for the sake of limiting variety; I really feel that's kinda against the CAP's premise. Sure, unpredictability can be broken in some (very very specific) circumstances, but really, Sketchy is going to be checked by the threats already outlined no matter what. Its STABs are just too easy to counter for mixed offenses to be threatening, even with a Shell Smash. I still think we should have lower SS, but that's because special on its own is more threatening for this guy than mixed. If this guy deviates from its standard sets to the extent that is can defeat a designated counter 1-on-1 (which IMO is something Sketchy should be able to do) then it's probably been warped so much to fill the niche that it's not going to pose much of a threat by itself anyway.
@anyone saying 'we need to keep this guy's stats low': just so we're on the same page, I hope you're not suggesting that we should keep the numbers low, or keep the BST low, in order to create an appearance of balance. Also, you should know that the "jack of all trades master of none" idea was somewhat shot during concept discussion; we want it to be good at various things, yes, but we want it to be able to effectively abuse the myriad powerful moves it has access to, that other pokemon cannot abuse effectively in OU (otherwise what are we doing). Also, if Sketchy isn't effective in top tier OU, then it's barely worthwhile making. Attempting to nerf the guy at every stage doesn't help,
lol anyway
PT: Good
ST: Very Good or higher really. (perhaps not Fantastic)
PS: Very Good or Excellent.
SS: Above Average
reachzero's reasoning for Special Tankiness being Very Good+ is my reasoning. Its defensive niche is primarily on the special side, so giving it a good rating here actually allows us to take advantage of the various non-offensive options Sketchy is gonna have access to, as well as bulky-boosting moves. There's also the least chance of breaking CAP2 if its bulk is biased specially; the few specially-based threats we've listed can OHKO it all the way up to Fantastic, so we might as well make it somewhat high and give Sketchy the best chance of being balanced that we can. This guy has such an interesting and possibly extremely useful defensive typing, I cannot stress that enough. Physical Tankiness should not be so low that it's worthless even with investment (Good is basically Jellicent-esque bulk), but being able to revenge kill this guy, be it with Priority or a Scarfer, is most often reliant on physical defense, so when uninvested, or after a Shell Smash, it ought to be quite low.
As for offenses, I've made myself clear. We aren't making this guy crazy broken by giving him anything short of Fantastic Physical Sweepiness, and he isn't boosting it either way, so we might as well give him off-the-bat potency. I'm leaning more towards Excellent myself, as it really lets you plough stuff down. This guy isn't outright sweeping with all-out attacking sets in all probability, even with coverage, so we should at least give him the ability to actually beat common walls, otherwise what's the point. When it comes to Special Sweepiness, we could probably go for Good as well, but I'm all for limiting it at this stage - make it too high and Quiver Dance would just dominate (although, lessening its Physical Bulk does actually make QD less dominating than you might think...).
Anyway, FINAL WORD (well not really)
Actual final word AKA edit: its weaknesses do not prohibit it from being a wall. The only weaknesses it has that really stand out are Fire and Dark, one of which is solved by Rain - Flying attacks are unfortunately very rare, Ice attacks are mostly unSTAB'd and specially based, and Ghost is basically Gengar who hates switching in anyway. It could make a very effective wall, or at least a very effective "bulky attacker" (lol) especially because of its delicious defensive niche. This guy really has a lot of potential for special walling. Also 'same across the board' makes no sense, as because of the disparity between the quality of each move available, and the effectiveness of the typing we've given it, if we give it the same physical stats across the board you're going to end up with a mon that is very biased towards something anyway (probably special attacking). Use the Celebi example: sure Celebi would always use QD if it had it, but, if its movepool allowed, would it use Gear Shift over QD? How about Sacred Fire? lolno