In a startling departure from LV's typical insistence on historical accuracy (yes, the ancient pyramids shot beams of light into the sky...didn't you see Stargate?), Mob Bar's exactly the kind of Prohibition-era speakeasy/supper club you would have found in Sin City had it been even been developed before repeal, meaning there're restored tin ceilings, period chandeliers, '20s glassware reproductions, and cocktail waitresses dressed in short red flapper dresses.
Speaking of cocktails, they fittingly trend toward whiskey & wood grain, including the Devil's Cut/Canton/falernum "Clara Bow", with Green Tabasco and fresh lemon; the Old Forrester/Aperol/amaro "Brass", with a dash of Bitter Truth's Jerry Thomas bitters; and their signature "Usual", a blend of Woodford, Cherry Heering, and Carpano Antica finished off with Angostura & orange bitters. You can also nab nightly rotating infused shots by opting to "Hit the Flask", a good option for those looking to get whacked.
Backing up the hooch'll be Italian small plates of pecorino & mozz risotto arancini, pre-forked spaghetti & meatballs, littleneck Clams Casino, prosciutto-wrapped Shrimp Spiedini, and Spicy Mussels Marinara, hopefully the only muscle you run in to (listen, there aren't that many mob-themed bars, so instead of groaning why don't you just shut up and read a few more mafia jokes??).
And if all this doesn't fill up your mob meter, not to worry: MB's located a short walk from the soon-to-open downtown Mob Museum, museums being exactly the places you'd find yourself at in Sin City were you not so dedicated to keeping things real by drinking Pina Coladas out of life-size plastic AK-47s.