Not that i am against moving Zard Y back up but i am realy not convinced about that defensive set. It basicly acts as a pivot and using a pivot with a 4x SR weakness seems counterproductive to me, sure it counters Mawile but tbh i would rather go for Heatran or even Arcanine before i resort to charizard for that. Aside from that i cant think of that many other physical threats that it could check with that 4x rock weakness, against slower attackers it might even get screwed by Earthquake when its forced to roost.
Is there anything else he can do that is notable?
In the first replay, Zard Y was forced out a ton and barely did anything; the things that it burned could have been OHKO'd by a normal Y or done better by a defensive X. Quagsire and Amoongus put in more work.
Second replay was a bit better as you burned Garchomp, but X could have done that too. You were still forced out a bunch, like when Mega Mawile hit you with Play Rough and let your opponent bring in Keldeo.
In the third one you probably would have lost Y regardless of Hax since your opponent had a Keldeo and Roosting each turn would waste your sun turns.
I just fail to see what Y does that can't be done better by X on Stall. It might not have as high a Spd stat, but that's what you have Chansey for. Then again I don't play stall so take that with a grain of salt.
EDIT: Okay yeah it counters Mega Mawile like
Baharoth said, but their are better ways of doing that without using up your Mega.
1st replays aren't me it was some guy at top of ladder few weeks ago (I like watching top players replays)
Being able to counter lando and mawile is huge with no other pokemon being able to do it.
The lack of item is actually nice as it allows it to stomach knock offs. hence it can also counter/check bisharp. Something Moltress its main competition can't do.
I know it can ohko things like mawile, but if it attacks it allows sucker punch to ko. Also wisp allows you to burn switch ins like garchomp and tyranitar.
Heatran gets beat badly by focuspunch also it hates knock offs.
As for keldeo 252 SpA Choice Specs Keldeo Scald vs. 248 HP / 160 SpD Mega Charizard Y in Sun: 150-176 (41.7 - 49%) Not sure how much bulk this zard was using, but SPD ZardY can even tank hits from keldeo
0 SpA Mega Charizard Y Solar Beam vs. 0 HP / 4 SpD Keldeo: 282-332 (87.3 - 102.7%)
Arcanine is nice, but besides countering mawile its pretty useless.
For defensive purposes zard still has an immense offensive presence.
And of course it gets forced out most stall mons do get forced out
In addition Zard Y is great vs other stall breakers like sabeleye mew gengar gliscor
As for megas on stall teams it only faces competition from scizor, aggron, venu, and zard x
Zard Y counters things no other mega or any other pokemon can in on pokemon.
This is just part of the reason it should move up. The other being its still a beast on force of nature type teams.
Obviously it has its flaws, but its flaws are what is holding it from S in my opinion not from A+