After laddering for a bit, I'm going to echo the crowds, and put forth my arguments for why we should further discuss, and potentially suspect certain abilities.
Water Bubble is able to do quite a number to the Balanced Hackmons metagame and is fairly overcentralizing in my opinion. We already have Adaptability, so there is little to no reason to have this unhealthy ability polluting the metagame. Water Bubble is mainly a concern with Satoshi-Greninja, Primal Kyogre, and Palkia.
252 SpA Water Bubble Primal Kyogre Steam Eruption vs. 252 HP / 252+ SpD Registeel: 130-154 (69.5 - 82.3%) -- guaranteed 2HKO
This is unboosted, and itemless, and yet it still has no switch ins. When a single ability makes things like Storm Drain viable (especially for Imposter checks), there is an overcentralizing, and unhealthy aspect to it in my opinion. I don't think calcs can really put into words how I feel about this ability, so I suggest people ladder with Water Bubble and form their own opinions based off of that, but I found this ability to be very unhealthy personally.
Moving on, Triage Mega Rayquaza causes some issues. It clicks one move (generally either Shell Smash, Substitute, or Spore) and wins, and it's fairly hard to check due to it outprioritizing everything. Generally Mega Rayquaza checks are bulky Steel types, occasionally bulky Rock types (notably Mega Tyranitar, Diancie, and to an extent Mega Diancie), or revenge killers, but Triage is able to undermine all of these. With priority Drain Punch, Mega Rayquaza is able to check Registeel easily.
+2 4 Atk Life Orb Mega Rayquaza Drain Punch vs. 252 HP / 4 Def Registeel: 330-390 (90.6 - 107.1%) -- 81.3% chance to OHKO after Stealth Rock
Aegislash is a notable check to Mega Rayquaza with Triage, but because Mega Rayquaza is so versatile, it might just drop to a coverage move, or have to deal with Substitute and Spore. Notably Queenly Majesty, Dazzling, and Psychic Terrain can deal with Triage Mega Rayquaza, but these specific checks struggle against non-Prankster variants, so Mega Rayquaza involves either punishable scouting, or game breaking 50/50's. Keep in mind that Species Clause doesn't exist in Balanced Hackmons, so if somebody felt like it they could easily run multiple Mega Rayquaza's to throw off an opponent, and allow one to wall break while the other one can simply sweep (not that a set up Mega Rayquaza requires much wall breaking beforehand due to it's unmatched base stats, and the insane coverage seen in Balanced Hackmons).
I don't think it's unreasonable for this to go on suspect once the metagame advances further, and it should definitely be looked further into. I'm sure there are other abusers of this as well, but Mega Rayquaza is the most notable one I've found. Perhaps Kartana may be able to abuse this to a smaller extent with Horn Leech.
This one is the least concerning to me so far, but Queenly Majesty, Dazzling, and Psychic Surge cause issues when dealing with certain set up sweepers. The -ate abilities have already been nerfed this generation, but now that you can block priority, certain Pokemon such as Quiver Dance Mega Mewtwo Y can abuse the lack of priority, and set up without remorse even when the opponent has a revenge killer.
Again using the example of Mega Mewtwo Y, it no longer needs to run King's Shield, and can not be outplayed nearly as well as could be achieved before. This means it can not only carry an extra move on it's arsenal, but that priority just in general can not touch it, allowing it to sweep a lot of teams just because it got in.
An example set that Mega Mewtwo Y could run is Psychic Surge, with Quiver Dance, Psystrike, Fire Blast/Earth Power, and Moonblast/Secret Sword.
252 SpA Mega Mewtwo Y Psystrike vs. 252 HP / 0 Def Giratina in Psychic Terrain: 237-280 (47 - 55.5%) -- guaranteed 2HKO after Stealth Rock and Leftovers recovery
We already see unboosted and itemless Psystrike 2HKO'ing Specially Defensive Giratina just simply due to the raw power of Psychic Terrain. Now consider that this can't be revenge killed without random Scarfer's (assuming Mega Mewtwo Y hasn't already set up a Quiver Dance, allowing it to outspeed them), and that it can destroy it's switch ins with overwhelming power running of off a base 154 Special Attack stat, and the much less limited movepool that comes with not having to carry King's Shield.
This feels like an unhealthy extension of Protean Mega Mewtwo Y, and should be looked at later on once the meta evolves in my opinion.
Later on, once the metagame further develops, Primals and Mega Rayquaza should probably be looked at as well, but these should be a much lower priority on the suspect scale than the three abilities listed above.
