Bug/Flying. Even if that group as a whole has maybe two decent pokes.
Even without Stealth Rock, which puts about three dozen nails into its coffin by itself, there are just too many weaknesses that a ground immunity, 4x fighting and 4x grass resist can't overcome. But Stealth Rock is definitely the most disheartening drawback of them all.
So, here we have Yanmega, with two extremely good abilities, the rarely used of the two being deceptively useful and fitting perfectly with specs (which is just fun) and the former being a strong hand in overcoming adversity out the ass; well, if it weren't for the fact that there's only one handhold for it to grab onto, which happens to be wobbly.
Unlike most bugs that share the now cookie cutter STAB options of Air Slash and Bug Buzz, it can actually use them plus a couple other basic TMs that can hit hard in the few events you'd use them.
And those stats! Only that SDef is pretty crummy. Sure that speed makes you shy away from the sexy Tinted Lens, but it's a step higher than the cutoff point for speed stats typically worth maxing (of course there's exceptions, but you know what I mean, right?)
I'll give Yanmega one thing, in that unlike other pokes with horrendous dual typings, it can at least be usable in some 3v3s, which sadly no one plays.
Felt like making this whiny topic after using Yanmega again, briefly, and noticing it has more going to waste based on its typing than other pokes that aren't particularly usable.