Ban Venomoth, and don't ban the others
Venomoth: You can lead with him and potentially win the match right there. It gets +1 speed thanks to focus sash/ favorable match up, sleeps somthing, sets up more and passes. Not to mention it is immune to fake out's flinch (with shield dust) and resists mach punch. If it was passing shell smash this may be a different story, but quiver dance is just unfair as it only gets easier to set up.
Yanmega: Very close to deserving a ban, but imo not quite there. There are several special walls that can take on Yanmega successfully, the tinted lens set is easily revenged, and stealth rock + smart play with a ghost type absolutely ruin Yanmega.
Omastar: Again, close to being worthy of a ban. However, as Heysup pointed out, it can still be revenged at +2 speed, is weak to priority, and some special wall can handle it.
Gorebyss/Huntail: It might just be me, but a decent team and smart play always gets me a win vs smashpass teams. Doesn't mean these two should be overlooked though.