Reqs:
http://tinypic.com/view.php?pic=984ylk&s=9#.V-rChSQllS0
Baton Pass:
BAN
The issue with Baton Pass is that is it one of the strongest archetypes in Mix and Mega, yet it can be pulled off rather easily compared to the likes of regular play styles. All one has to do use this strategy:
1. Find an opportunity
2. Set up with correct move
3. Pass to an -ate or Blazikenite sweeper
To combat Baton Pass you just have to prevent one of these 3 steps. For most teams, countering Mew is done by preventing step 1. These are methods such as offensive pressure with Mold Breaker Taunt Leads (or any user) or sheer offensive pressure through wall breakers. However, usually strategies like these end up failing due to something random like mew using U-Turn on Hoopa-U (lol) or offensive momentum shifts. After the offensive pressure is gone, Mew + recipient will win.
To stop Mew in step 2, using hard checks like dragon tail Primal Groudon or Mold Breaker Roar will work. Again, these counter plays can be stopped by Mew's own counter plays such as Taunt or Substitute. One of the most underrated methods is of stopping mew here is setting up a substitute. This prevents mew from going to step 3 since the recipient must tank a strong hit from something like Keldeo. To beat this, mew would have to carry defense boosting moves for either special or physical depending on the threat.
Step 3 has a huge number of counter plays. Primal Groudon is one of the best as it usually just beats the recipient 1v1, Blue Orb Skarmory can phase the recipient, Ditto can counter sweep, bulky Landorous-T and faster priority. Although stopping it this step usually results in a trade-off, Mew now has 1 less recipient for passing boosts and if this keeps up, eventually Mew will be the last one left, completely helpless.
Overall, the methods of beating Baton Pass are certainly plenty, but it requires overly careful team building to stop such a basic yet insanely effective threat which is not good for the meta. There is a feeling of unfairness when fighting baton pass since the strategy is so simple and hard to beat compared to the complicated strategy your own team is constructed upon.
Gengarite:
DNB
Gengarite is a tool for teams to remove specific threats. This is not broken by any means because good Ubers based teams use synergy, pressure and check threats in a collective manner. Removing a single threat should not damage the overall structure of a team. Gengarite does not invalidate any play styles either. The team simply must take a collective effort to check Gengar and weary that it may not even be holding Gengarite.
Balance can still make solid teams that still function well even with the omnipresent threat of Shadow Tag. The meta will simply have to stop using extremely vulnerable Pokemon like Blissey and Clefable, or at least without pursuit. And this is by no means a bad thing, in any meta there will be unreliable Pokemon.
Moving onto Gengarite's impact on stall, the meta itself does not exist and if it does exist, it is bad. There are too may things that rip stall apart like Tough Claws Garchomp, Adaptability wall breakers (Terrakion/Keldeo), Hoopa-U, Swords Dance Primal Groudon, ect. It is not Gengar's fault that stall sucks.
Gengarite does not threaten offense at all. The best thing it can do is trap and kill something like Pixilate Entei and get killed right after, unless you carefully time a destiny bond. In fact, offense can usually safely assume it is always Pidgeotite.