Mega Slowbro is a great mega for stall but the biggest disadvantage is that you can't use Mega Sableye.
This is one thing that really troubles me about Mega Sableye. What reason is there for a stall team not to run it? The benefits that it grants in terms of team support alone are greater than the benefits that many individual stallmons give to their team in terms of synergy, hazard control, and other team support capabilities.
In other words, many stall teams could just find a pokemon to replace with Mega Sableye; it might not synergise quite as well, and you may find yourself weak to particular threats, or lacking particular hazards, but Sableye's team support would more than make up for it and, experimentally speaking, you should win more as a result. Pokemon whose roles overlap with Sableye, or cannot be run alongside Mega Sableye are particularly at risk of this. I don't think there's any other pokemon that offers such powerful and universal support to stall teams in general. If it's difficult to visualise, think of the support that Politoed gave rain stall teams in BW1, though this example is more specific and clearly more dramatic.
Since Sableye is a primary pokemon in this sense, I think it should be the case that (and we may see in the coming months) the best stall team is Sableye and five mons to support Sableye.
I don't think this is good for stall; it may certainly help stall win more when people are not stacking fairy wallbreakers or running Skill Swap Azelf, but it doesn't bode well for inventiveness or novelty in a playstyle for which these qualities have been notably effective, when present. And it certainly doesn't bode well for the stall player's opponent, and their team variety, if in every battle Sableye is
always the primary threat to eliminate or weaken.
As a stall player I'm personally far more concerned about Sableye's detrimental effects on the metagame than Greninja's (but don't intend to start a Greninja discussion). In vague terms, it's generally accepted that Greninja, with its speed and power, threatens most the teams that run neither bulky walls that aren't 2HKOd by its attacks, nor multiple pokemon capable of revenging it. It is comparatively a minimal threat to teams that do run these pokemon. In similar terms I don't think it's unfair to say that Sableye, with its ability and durability, threatens all teams that rely on hazard damage or to a lesser extent rapid spinning. For both offense and stall the former is absolutely crucial, and against a stall team balance too can't do without hazard damage. Sableye threatens the entire metagame, and I think (though this may in the future prove false) the reason it is not currently seen as a primary threat on the level of Greninja is comparatively low usage.
I used "primary" in previous sentences to mean not just 'most important', but moreso 'first'. It is the first pokemon that any stall team should consider in order to be most successful, and it is the first pokemon that any opponent must consider in order to be most successful at winning. Idk about other stall players, but myself, I don't really like this.
What kind of pokemon do you use? Rhyperior or hippo? Unaware clef? I could use some ideas
I've been quite liking Diancie @ Shuca berry with a spread of 252 HP / 240 Def / 16 SpA Relaxed as a check to most birds and some dragons. The lack of recovery unfortunately means that although it can switch in to Talonflame repeatedly, some of the stronger birds (Pinsir is a bird right?) can only be checked once or twice. But its fairy STAB forces out he-who-shall-not-be-named, so that Diancie can set rocks.
