Oh cool, Leader's Choice.
I haven't figured out the optimal sets for this, but I think a FEAR strategy (to recap: a Level 1 mon that users Endeavor and Leech Seed in conjunction with Sturdy to cheese out KOs) could actually be viable. The only thing every FEAR team would autolose to is Skill Link; every other way of getting around the strat has a way to negate it. A major beneficial change this generation is the absence of Poison Heal, which could outheal residual damage from Leech Seed and weather.
Four abilities seem 100% mandatory: Sturdy to live hits, Flower Veil to avoid status (meaning you should have a Grass-type FEAR mon), Oblivious/Aroma Veil to get around Taunt (and other moves, in Aroma Veil's case), and Pixilate/Refrigerate/Scrappy to let Endeavor hit Ghost-types. Since Comfey is the only Flower Veil user, it's the only strictly mandatory mon on these teams.
At this point, Regenerator can still stall you out by just switching around; burn or poison will stop some of them, but not all of them. The way I see it, you can run a trapping move (i.e. Infestation) to stop that, or a Snow Warning/Sand Stream user to bring them down immediately after Endeavor. None of these are perfect strategies -- Infestation takes a turn to set up and doesn't help you keep your Sturdy, plus not many FEAR mons get a trapping move anyways. Weather forces you to either use mons immune to that particular weather or give up your item slot for Safety Goggles. Overcoat would work, but as discussed below, it limits your other options.
You can deal with hazards in one of two ways, I think -- either use a few extra moveslots on Magic Coat/Defog/Rapid Spin, or put Heavy-Duty Boots on your FEAR mon. While the first strategy seems appealing, you are usually not going to be using threatening mons, and might not get free turns to use Defog or Rapid Spin. Magic Coat is cool, but obviously it does not remove existing hazards. HDB will do the trick, I think; its main downside is that it precludes using Safety Goggles, which leaves some of the better FEAR users weak to opposing weather if you don't have Overcoat.
The last thing that I can think of which would stop a FEAR strategy is Rocky Helmet, Iron Barbs, and Rough Skin. Stuff like Static and Flame Body are circumvented with Flower Veil, but the only ways around contact damage are Long Reach Decidueye and Protective Pads. Leech Seed won't help you against Ferrothorn or other Grass-types, either. Your team slots are really constrained already, so I think Protective Pads are better, but frankly both are very constraining.
Suffice to say, I think this is at least a team structure that players should be aware of while teambuilding. On paper, it has the tools it needs to play around most strategies (except Skill Link, which laughs in its face). Only battling will tell whether it's actually good.
Or maybe this was already discussed upthread. IDK. I'm not reading all 23 pages of this.