Mega Scizor's best set in the Maison consists of Swords Dance, Bullet Punch, Bug Bite, and either Roost or Superpower in the last slot. Roost is more common, because it takes advantage of Mega Scizor's bulk and lets it set up more easily, but Superpower hits Steel-type Pokemon that would wall the set otherwise, like Magnezone, Cobalion and Registeel. As for the EV spread, you must give it max attack, and enough speed EVs to outspeed a certain threat to your team, if needed.
Here is Snail489's Speed Tier List for the Maison, for reference. The rest should go to HP.
Also, a few helpful links:
-
VaporeonIce's Threat List for Singles
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The pokemon sets in the Maison by Team Rocket Elite and Kaphotics
-NoCheese's guides for Singles(
here and
here)
And finally, welcome to Smogon!