http://replay.pokemonshowdown.com/mixandmega-442392177
Every mega is a non-standard one, and that makes this replay even more special.
Swampertite Politoed isn't the worst idea ever since you set your own rain to abuse with Swift Swim. Despite being a cool concept, though, it's not very good in practice due to poor stats.
Altarianite Mega Metagross is interesting and pretty non-terrible since Steel/Fairy is great defensively. Sheer amount of Fire in MnM undermines that though.
Charizardite X Weavile is terrible (since you lose the powerful Ice STAB that is the whole point of using Weavile in MnM, plus what are you even doing for Dragon STAB, and both STABs are shut down by Fairy), and Pinsirite Snorlax makes you ask questions.
Edit: Weavile doesn't learn even one Dragon-type move. No, not even Dual Chop.
Lapras is a Pokémon that I always really wish was good, but unfortunately isn't.
Edit:
http://replay.pokemonshowdown.com/mixandmega-442338383
Right is on a next level of bad. Someone take this one.
(R) Standard Mega Gallade.
(R) Mega Gallade running Close Combat/Thunderbolt/Synchronoise/Hyper Beam. Also, Synchronoise ever.
(L) Audinite Hippowdon. I guess they're really afraid of Terrakion. If they don't have an Altarianite user though they should be running Altarianite Hippowdon instead. Smaller defensive boost (+20 Def/+0 Sp. Def instead of +40 to each), but it'd actually get a physical Fairy move to use and boosted Attack.
(R) Keldeo trying to use Aqua Jet on Hippowdon. I don't care if that's SE, with Keldeo's Attack and Aqua Jet's base power that's going to do nothing to Audinite Hippowdon.
(R) Keldeo trying to Aqua Jet with Desolate Land up. How have people not yet learned how these weathers work?
(R) Switching Keldeo out after it takes 78% from Red Orb Togekiss's Dazzling Gleam… and switching in Salamence to replace it. That's not an improvement.
(R) Primal Groudon trying to Eruption with Primordial Sea up.
(R) Twice.
(R) Using Eruption at 50% health.
(R) Mega Kick Primal Groudon, which it uses on Skarmory for a whopping 12%.
(R) Primal Groudon reveals Thunder, finally taking out Skarmory. That's silly on its own, except as a niche counter to Blue Orb users. So, when confronted with a Blue Orb user, why try
everything else in your set first?!
(R) Primal Groudon using Eruption at 11% health.
(R) Keldeo tries to use Aqua Jet on Audinite Hippowdon.
(R) The opposing Mew used
Gunk Shot! It's super effective! Togekiss lost
39% of its health!
0 Atk Mew Gunk Shot vs. 248 HP / 8 Def Red Orb Togekiss: 152-180 (40.7 - 48.2%) -- guaranteed 3HKO
Something is wrong here.
(R) Gallade uses Thunderbolt on Togekiss. Not that it has any better moves to use.
(R) To their credit, their Zoroark actually has full Sp. Atk investment. Its Flamethrower does nothing to Red Orb Togekiss anyway.
(R) The opposing Keldeo used
Secret Sword! It's not very effective... Togekiss lost
11% of its health!
0 SpA Keldeo Secret Sword vs. 248 HP / 8 Def Red Orb Togekiss: 51-60 (13.6 - 16%) -- possible 7HKO
Um… physical Keldeo stat spread? Why aren't you running Sacred Sword then? Ignoring the fact that physical Keldeo is terrible every which way, of course.
(R) Only Mega on their team was Mega Gallade. That's an even bigger fail than all the teams made up of nothing but standard Megas.
Edit 2: Must be physically defensive Togekiss, since Keldeo shouldn't be able to deal damage that low with Secret Sword even with 0– Sp. Atk.