Nidoking, Nidoqueen, and Clefable should get Flamethrower over Fire Blast. In the case of all three of them, the primary targets of their Flamethrowers are all hit hard enough by that to the point where it's not really worth sacrificing both PP and accuracy when the power ends up being overkill more often than not.
Seviper gets Swords Dance, which is a possible option over Coil as it really doesn't have time for bulky boosting and would rather get its Attack up as quickly as possible.
Zangoose would possibly rather have the AoA and coverage of CC/Facade/Knock/Quick Attack than SD.
Quagsire/Gastrodon should always have Recover. There's really no reason not to run recovery on either of these mons that both have it and are both especially hindered without it. Additionally, neither have much reason to run Life Orb, especially Quagsire.
Umbreon should always have Foul Play; with out it you literally cannot touch:
Steel-types
Poison-types
Espeon
Xatu
Substitute users (most of which are faster Psychic or Ghost-type Pokemon that you'd comfortably beat with it)
Taunt users for the same reason as Sub
And more
Mega Aggron should always have Stealth Rock. Like Quagsire and Gastrodon with Recover, there really isn't a reason not to have this move on Aggron. Additionally, Fire Punch could be added to its moveset for the Bug/Steels and Ferrothorn that you traditionally do well against but lack a move like that to KO them outright.
Heliolisk and Pyroar don't need their respective weather moves. On both of these mons it ends up being a wasted moveslot, especially on Heliolisk when it gets Rain Dance/Volt Switch/Hyper Voice/HP Ice and ends up lacking something like Surf or Thunder to actually take advantage of the rain. It should keep Surf, but Thunder and Rain Dance should be eradicated from it's movesets, with Grass Knot and Focus Blast coming to mind as coverage moves that it can run instead. Additionally, if not already, Life Orb should be in its item pool along with the already existing Choice Specs. As for Pyroar, the corresponding Sunny Day and Solar Beam should be removed, with Hidden Power Grass maintaining the Grass coverage and Flamethrower as a secondary STAB being more ideal here. At the very least, they could use Life Orb over the weather extenders on their weather sets.
Double-Edge can probably replace Return on Mega Glalie. Like a lot of these mons previously mentioned you want all the power, and the recoil is not gonna end up mattering too much with a poor defensive typing and mediocre bulk.
Remove Mind Blown from Blacephalon. If it doesn't OHKO, which it actually won't on most things without a couple boosts, you will more than likey just lose your Blace. It already gets Fire Blast occasionally, so unless you're Calm Mind with Firium Z, Choice Specs, or some sort of AoA set, Fire Blast is always better. Even then, on the latter two you'd be running both Fire Blast and Mind Blown. Additionally, Fire Blast would be serviceable on Firium Z Calm Mind sets. Don't even get me started on that horrible, horrible amobination that is the Trick/Calm Mind/Mind Blown/Shadow Ball set that appears more often than it should. Can't reliably Calm Mind unless you Trick the Scarf away, and as stated earlier if Mind Blown doesn't OHKO whatever you hit then you basically die, meaning the only move you can reliably use while keeping Scarf is Shadow Ball, which is less than ideal unless it's relatively late in the game.
