First back to your original post, yes fog bank is worth the slot, especially if you're going for Elbrus because it either locks down their early game attacks or else it just draws out their removal so they've got to waste a kill spell on your fog bank rather than your flipped Elbrus.
Now to TyWooOneTime's post: I could see trepanation blade being a really good card for several reasons, if you get it out early game it completely screws over their land draws, i've seen people stuck most of a game with 2 lands because the top lands always get milled. The pike isn't nearly as effective in this build, there are 6 total instants/sorcerys in the deck so in an average game there'll be 2-3 in the graveyard, and that's really late game when you want to be swinging for lethal not for 3 damage.
As far as making Withengar Unbound unblockable, it doesn't really seem needed, he can only be blocked by black or artifact creatures with flying, basically his only fear would be Vampire Nighthawks but then you're probably better off just giving him first strike so that you gain board position while dealing most of the damage anyway.
I have been attending FNMs at my LGS along with some other assorted days pretty frequently lately and I've come to realize that there's two ways to look at it, either you drop cash and Net-Deck, you start with a basic deck and use FNM as a way to improve it, or you throw something crazy and fun together every week to throw people off, I do a combination of the last two, I have a couple decks that i've used there, a UW infect exalted deck that throws people off, a couple different mill decks, self mill and opponent mill, and then my deck that I'm actually trying to make really good, which is a little more boring design wise but I like winning from time to time and I've found that I can trade for extreme profit at my FNM, which lets me get the cards that I really want for my decks. Overall I'd say that building decks to keep people guessing is the most fun of the 3 but I've never actually Net Decked so I can't speak to that.