I think in PvP, if Legendaries are allowed, and I assume species clause, based on the original trailer, people can battle in groups, and there will be a hierarchy of who is the best to use.
I believe Rayquaza>Kyogre>Mewtwo>Groudon>Articuno>Tyranitar will be common place.
Articuno seems like an odd choice, but it helps counter the most common sets of Groudon, Rayquaza, and isn’t afraid of Solar Beam. Tyranitar might seem like the only option for Mewtwo’s Shadow Ball sets, but Rayquaza will bode well for its Focus Blast sets. Tyranitar’s Stone Edge can also seem useful for Articuno and Rayquaza. I didn’t list Raikou or Entei because they are more easily hardcountered by Groudon and Kyogre due to suffering from both quick and Charge moves.
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Also, according to Gamepress, Aggron as being just as bulky as Blissey against Rayquaza when factoring even the full average of all of its movesets, and surpassing her with the highest TDO... period.
They go on to
Name it as a top Counter, factoring it’s unique Typing, while having a higher Attack stat, Super Effective Dragon Tail, and STAB Super Effective Stone Edge. This is based on TDO, in dealing damage before being KOed, rather than DPS.
(Gamepress defines an anchor not as a Pokémon that walls with no offense like Chansey, but as a Pokémon that lives long enough to outdamage a Glass Cannon by virtue of dealing more total damage over a longer period [slower but pays off] before it dies such as Lugia instead of Alakazam for Machamp raids)
