Hidden Power Fairy is not a move, yea.
Anyway, Acid Armor Reuniclus teams are meant to have a means of crippling Tyranitar and Greninja through status (Toxic Spikes being far-and-away the most common method of doing so, being essentially a staple on builds with Acid Armor Reuniclus). Because of this, Toxapex is seen on a vast majority of Acid Armor Reuniclus teams; the fact that Reuniclus + Toxapex is used makes the team a bit inherently passive or at least easy to take advantage of for specific offensive threats such as Z Heatran, Mega Mawile, SD Kartana, and even Tapu Lele. This makes builds around Acid Armor Reuniclus quite limited as you are forced to run specific things (you find a lot of utility Mega Latias for covering Heatran, Kartana, and potentially Defogging, you find a lot of Magnezone to eliminate Mega Mawile, you find a lot of AV Tyranitar for making Tapu Lele's existence harder, etc.). Acid Armor Reuniclus has a lot of viability, but structures with it are limited, thus making it challenging for less experienced builders or those looking to explore the intricacies of the metagame. There are only a limited number of balance builds that you will see with Acid Armor Reuniclus and most of them have already been built and used in tournaments, so perhaps look for those games if you want examples.
As for other Reuniclus (2A + CM + Recover, usually with a Z move), however, the boundaries expand quite a bit. This does not come without specific choices and inconveniences though. You want to run Focus Blast to hit Tyranitar, but then you are walled by Mega Sableye. Oftentimes, this leads to midground coverage moves such as Signal Beam, Flash Cannon, or even Energy Ball being ran. On top of that, moves such as Shadow Ball and Thunder have been seen in the fourth slot. The Z move can be slapped on as the type of any of the secondary coverage moves or Psychic; Z Psychic does a ton to just about anything at +1 and it poses the largest threat to Unaware Quagsire and Clefable on Stall aside from the moves that hit them super effectively (Energy Ball and Flash Cannon respectively). It is still most common on balance and you will oftentimes see similar partners -- Thunder Wave Mega Latias to cripple Tyranitar, Magnezone to remove Mega Mawile, who can otherwise take advantage of more passive Reuniclus cores, and even Toxapex will get the nod on plenty of Reuniclus balances regardless of AA or 2a. This is far from fully explored territory at this point and I feel like the options are limitless, so perhaps there will be more of this in the future, but as of late it feels like Reuniclus usage and exploration has plateaued after starting to trend with the AA set during late WCOP and into OLT, which made sense seeing as AA's best characteristic is sweeping the physical set-up heavy HO teams that everyone spammed on the ladder. Anyway, Reuniclus is hard to build with, but it is very possible to do, so don't give up!