Hey there! Your team definitely has some glaring flaws with the sets you chose as pretty much every pokemon has, in some way, sub-optimal moves that don't do anything noteworthy compared to better moves they could use. In addition, some pokemon have items or moves that may be useful for some teams, but not this one. I believe that once the sets are patched up, there's actually a decent foundation to work with. Kyurem-Black, I think, makes for a decent partner with Mega Scizor, as Icium-Z Kyurem-Black is able to threaten many of Mega Scizor's defensive checks such as Ferrothorn and Toxapex, allowing for Mega Scizor to have an easier time threatening opposing teams. You also have some pivots like U-Turn Greninja and Rotom-Wash to bring in Kyurem-Black to wallbreak. Alongside an overhaul of the movesets, here are some replacements that I think will help make the team more cohesive and provide more support to this Kyurem-Black + Mega Scizor idea.
First, I suggest replacing Toxapex with Tornadus-Therian
Tornadus-Therian @ Rocky Helmet
Ability: Regenerator
EVs: 252 HP / 4 Def / 252 Spe
Timid Nature
- Hurricane
- Knock Off
- Taunt
- Defog
Having Rotom-Wash and Toxapex on the same team is pretty redundant since they largely check many of the same things and share many of the same weaknesses, so I felt like I wanted to keep the volt-turn element to this team and replace Toxapex rather than Rotom-Wash. The matchup against offensive Fighting types like Mega Medicham and Mega Lopunny were pretty bad since there was little on the team to respond to them. Rotom-Wash can live a hit from these pokemon from full and use Will-O-Wisp (which you don't have on your Rotom, but I'll be changing that), but it's very easily chipped into range of being OHKO'd. Mega Scizor suffers from this as well, in addition to the fact that it can't revenge kill any of these pokemon with Bullet Punch without a lot of prior damage. Tornadus-Therian gives you a more reliable answer to these threats by being able to revenge kill them. On the right prediction, it can even switch into these threats, but there are some caveats to this. Mainly that Medicham and Lopunny often carry Ice Punch as coverage. Lopunny in particular outspeeds Tornadus and can take it out with High Jump Kick + Return with some prior damage. So, it's not a 100% guarantee of safety, but it's something. Tornadus-Therian also provides another Ground immunity, which eases some of the pressure on Rotom-Wash to perform that role. I opted for Taunt over U-Turn because I figured it would help against the stall and balance matchup, which isn't all that great outside of Kyurem-Black. Plus with Greninja and Rotom-Wash forming the Volt-Turn core, it's much less necessary to have U-Turn on the Tornadus for this team.
Next, I opted to replace Chansey with Gliscor
Gliscor @ Toxic Orb
Ability: Poison Heal
EVs: 244 HP / 52 Def / 76 SpD / 136 Spe
Jolly Nature
- Stealth Rock
- Earthquake
- Toxic
- Roost
I don't particularly like Chansey on more offensively geared teams because I think it saps momentum from the team since it just sits there and sponges hits without any offensive presence. I think having an Electric immunity is really good for most teams so that you don't get overrun by teams that utilize Volt-Turn cores of their own. Gliscor provides that immunity. Gliscor also provides Stealth Rock, which your team did not have (Chansey could learn it, but you didn't have it on that pokemon). Stealth Rock is a pretty important hazard for teams to have, so I feel that pretty much every team should have something that runs it. I chose Gliscor over Landorus-Therian to help the team out against Heatran a little bit since Gliscor's recovery in Roost and Toxic Orb + Poison Heal makes it easier to switch into moves from it. You just have to be careful of Z-move variants since they can easily knock out Gliscor with any of the Z crystals it commonly uses. You can try defensive Landorus-Therian instead if you want, since its Intimidate ability really helps against physical wallbreakers that can potentially give this team trouble.
Now onto the moveset changes. Starting from the top, I suggest making Greninja the Choice Scarf set instead of Focus Sash lead.
Greninja @ Choice Scarf
Ability: Protean
EVs: 176 Atk / 80 SpA / 252 Spe
Hasty Nature
- Rock Slide
- U-turn
- Ice Beam
- Spikes
Focus Sash on Greninja can make it into a viable hazard stacking suicide lead, but this is pretty much only good for hyper offensive teams that basically run 1 hazard lead + 5 sweepers/breakers, which this team isn't. Your team didn't really have any speed control outside of priority which made it susceptible to various offensive threats that can outspeed your pokemon. With Choice Scarf, Greninja is able to act as a very fast revenge killer that can even outspeed many other scarfers like Kartana and Landorus-Therian. Volcarona was looking like a big problem since I couldn't think of a way to add defensive checks to it as replacements, so Rock Slide is used to revenge kill it (it also has the added benefit of hitting other things like Charizard-Y). the 80 SpA EVs is to ensure that Ice Beam OHKO's Kartana with the rest put into Attack after the Speed EVs are maxed.
With Mega Scizor, I don't think Pursuit fits a niche this generation like it did in ORAS OU. I think it generally benefits more from one of U-Turn, Knock Off, or Superpower. Knock Off is what I ended up settling on. Also, I'd rather have Scizor EV'd more defensively for this team since it's the main answer to Fairy and Psychic types with Chansey gone. The standard spread of 248 HP / 16 Def / 244 SpD with an Impish nature should be fine.
With your Rotom-Wash, I don't really like the dual status on it. I think Will-O-Wisp as the status move works best here since it can cripple physical attackers, some of which can be threatening to the team without it. I would also have Volt Switch on it, since part of its niche as a defensive Water type is that it can act as a slow pivot with that move to safely switch into other things. Sucker Punch is pointless due to its extremely low Attack stat and the fact that it doesn't hit anything noteworthy. Against faster offensive threats, you should try switching into something that can take it on if possible rather than trying to combat it offensively with Sucker Punch. Leftovers is fine on it, but I'm changing the item to Wiki Berry since the 50% HP regain is really nice for checking pokemon like Greninja. Regarding the EVs, I'd say that if you're not running a simple 252/252/4 spread, you should have a specific purpose for giving something a particular number of EVs. Your mixed 128/128 Def/SpD EVs don't seem to do that. Once again, I'd just go with Smogon's spread of 252 HP / 200 Def / 56 Spe with a Bold nature. The speed EVs are enough to outspeed Adamant Tyranitar with the rest being put into HP and Defense to help it take on physical attackers that it can check. Same thing goes for the moveset. Hydro Pump / Volt Switch / Will-O-Wisp / Defog should be fine. You could go with Pain Split over Defog if you feel it's necessary, but I like the utility of having a second Defogger here. It's nice to better ensure that Kyurem-Black can enter the field without taking unnecessary Stealth Rock damage since its typing makes it lose 25% of its health after rocks. Speaking of whom, let's move onto the next and final pokemon to discuss.
With Kyurem-Black, I prefer having the Icium-Z set since Subzero Slammer with Freeze Shock can knock out or heavily damage a lot of Mega Scizor's checks, such as Ferrothorn and Celesteela, immediately. Life Orb is a viable option for it, but I feel like Kyurem-Black's the best Z-move user for the team. Shadow Ball doesn't hit anything important. Earth Power is the preferred choice here for coverage since without it, Kyurem-Black can't touch pokemon like Heatran that resist its STAB Ice Beam and don't take much damage from Fusion Bolt either. Roost, while very useful for its ability to improve Kyurem-Black's longevity, I think can't really fit since the Z-move set needs Freeze Shock and I think the coverage from Earth Power is too good to pass up here. The moveset, then, would be Freeze Shock / Ice Beam / Fusion Bolt / Earth Power with a spread of 252 Atk / 4 SpA / 252 Spe and a Naive nature. Max Attack for giving Subzero Slammer the most amount of damage with Freeze Shock.
Here's the importable for the team with its final changes.
Admittedly, I think there's quite a few things in the metagame that can potentially overwhelm this team like Mega Mawile with Fire Fang and Hawlucha, but it's not completely impossible to win against them. Hopefully for the few changes I made as far as replacements go, this works out much better for you than your current team! Still, though, if you don't mind having more changes to the team, you could try using Tapu Fini over Rotom-Wash. It gives you a more reliable switch-in to Greninja as well as Heatran so you can run Landorus-Therian over Gliscor without too much of a drawback. Fini is also a more reliable Hawlucha answer since Rotom-Wash pretty much can't take any damage if it wants to check Hawlucha. The team with those changes could look something like this.
