Updated suggestion teams with Psyshock Starmie, made a brief mention of other megas that could take on 'Zard Y.
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Flygonial
Adamant Zoroark
Mega Latias as you mentioned in the thread would probably be good regarding Megas that still take on Zard-Y - I'm not necessarily sure how it would fit in though (straight-up over Ampharos and the team loses a good Torn-T switch-in; over Starmie and no hazard control unless the Ampharos replacement covers that)
Flygonial
Honestly, I'd be more on board with Mega Aero or 'Zard X, problem is the former needs to be bulky to be a good switch-in, but it could work out if I take your other suggestions.