Now obviously Aegislash, Mimikyu, Morpeko, and the Weather Trio's Rogue Battle gimmick are all replicating their Abilities.
Tatsugiri & Dondozo is also sorta, though since there's no Double Battle when Dondozo is sent out the Tatsugiri on your team just hops out and enter its mouth to command it (and works as Commander usually does). Still, it this just a work around because there's no Double Battle, or is this maybe something new to Commander for the main game so it has a use in Single Battles?
In addition to MRX receiving an Attack boost from Volt Tackle, the Swords of Justice raise BOTH their Atk & SpA when they use Sacred Sword. Their only Ability in the main game is Justified which raises their Atk when hit by a Dark-type Move, so if this is hinting at a new Ability for MRX then it may also mean a new Ability for the Swords of Justice (and a better one from the sound of it). Since Secret Sword isn't in ZA, I'm going to guess if this is hinting at a new Ability for the SoJ, it'll likely also increase offense when Keldeo uses Secret Sword. Though, will it be both Atk & SpA, or is that just for Z-A and maybe Sacred Sword would only increase Atk (or, while Sacred Sword increases Atk & SpA, maybe Secret Sword would increase SpA by 2 stages)?
And interesting only Mega Raichu X have this trait. If this is a new Ability, then what is Y getting if it's not a stat increasing Ability (and why wouldn't they program it in as a sneak peak like X; unless it's just getting an existing Ability they don't want to have to program other Pokemon to also have)?