Weakness Cup announced: participants get Ampharosite, Altarianite and Lati@site

And just when you thought the previous competition had ended, another one starts up! This time it's the Weakness Cup, and participants will be awarded with the Ampharosite, Altarianite and Lati@site mega stones! As usual, you need to do at least three battles to get your place on the rankings. Registration begins on the 20th July at midnight UTC, and battles go from the 28th to the 30th of July.

Rules
Double Battle format, 4v4
The entire National Pokedex is available
No megas or Z-moves! In fact, many items can't be used! Only the Weakness Policy and type-resisting berries can be used, such as the Yache Berry.
All Pokemon must have at least 5 weaknesses
All other rules apply

Here's a spreadsheet that I made, which lists all Pokemon that can be used, along with their stats. It should be a useful resource for teambuilding! How are you guys going to go at this competition?

I'm not going to participate in the event, but it'll be interesting to see how the released Megas will perform in OU. Mega Latias will be useful for checking Volcarona without Bug Buzz, Zapdos, Mega Charizard Y, Keldeo, Toxapex, Mega Manectric, etc. However, Pursuit users are somewhat prevalent right now. Not to mention Magearna and Celesteela are very popular. It's worth noting that Calm Mind Mega Latias beats Assault Vest Magearna, though. Unlike in ORAS OU, Keldeo is usually Scarf and not major offensive threat anymore. Volcanion, Thundurus, and Tornadus-T aren't as common either, so that's less Pokemon for Latias to check unfortunately.

Mega Ampharos's uses seem even more niche in SM OU than they were in ORAS OU. Still, it checks Mega Charizard Y, Electric-types, and Celesteela, which counts for something. It's a decent blanket check to special threats in general like Gengar, but it's worn down easily.

Mega Altaria's outlook doesn't look too great. Dragon Dance Altaria is countered by Celesteela. Clefable, Mega Scizor, and Mega Venusaur are all still around like in ORAS OU, though Clefable isn't as common. SM OU has a higher abundance of Scarf users, especially Tapu Lele, Nihilego, Kartana, Greninja, Gengar, Excadrill, Jirachi... Altaria's special set might prove to be more effective. We'll see.