Mega Scizor appreciates Stealth Rock support, which can knock various Pokemon into Bullet Punch KO range, so I started with a Landorus-T and Mew lead to ensure Stealth Rock can get set early on in most matchups.
Standard-ish bulky Landorus-T set, but I gave it a Red Card for a new twist. In a lot of games Red Card won't do too much more than annoy your opponent for a turn, but it's actually nice to have in your back pocket as a phasing technique against runaway sweepers like Weakness Policy Diancie at +2.
Landorus-T's main goal is just to set Stealth Rocks, but it can Earth Power stuff as it needs to. Gave it Protect > another coverage move because I really wanted Lando-T to be reliable at getting the rocks up, but that's just a preference thing.
E: also gave Landorus-T 72 Spe EVs to outpace Mega Metagross after an Icy Wind.
Mew's primary role is to be a fast Fake Out lead to help ensure Lando-T gets rocks up on Turn 1. However, beyond that Mew's options are wide open on this team. Super Fang is super threatening in the early game; chipping all targets for 50% with no regard for a type chart is no joke, and Scizor appreciates all the softened up targets in the late game. Icy Wind is self explanatory, but really great on Mew and I'm surprised more people don't run this.
Incinerate is another really neat tech that really throws a wrench in teams that over-abuse pinch berries, and it also hits Kartana / Ferrothorn for some decent chip damage. Changed Incinerate to Energy Ball to deal with Gastrodon. Incinerate's still cool but more of a "nice to have" than anything Mew misses in most matches. Also moved 12 EVs to SpA so Energy Ball is always a 2HKO.
The next thing that came to my mind was that this team needs to be as hostile as possible to Fire-types, since Mega Scizor really hates them. That's where Araquanid comes in. It can stand up to pretty much every Fire-type in the meta besides Volcanion, and the utility it offers is fantastic as well. It also offers some resilience against Trick Room builds, which I wanted to make sure I was prepared for.
Tapu Koko is here mainly because I still needed a Tapu and I wanted sleep immunity. I went with a Modest Electrium set, which is very powerful and makes quick work of bulky waters that otherwise annoy this team a bit. Taunt for a bit of anti-Trick Room and anti-BS support, since Mew can't always be on the battlefield.
Incineroar does Incineroar things, but also has Roar as a phasing technique and hard answer to Trick Room. Having two Fake Out users is also just great for keeping momentum up during a match.
And finally, we have Scizor! It's a completely standard set, but the rest of the team compliments it well and, in turn, Mega Scizor offers the team a late-game wincon and a defense against some potent threats like Diancie.
Overall, I'm really happy with how this team turned out and like I said I won 3/4 games of a roomtour with it so I feel pretty good about how this game plays against different matchups.
Enjoy!