Mantis is back etc

Definitely don't use Sacred Sword over CC. The extra power is infinitely more useful than keeping its defenses "strong." You'll need a lot more prior damage to break down walls like Skarmory and Hippowdon (if your Balloon has popped) if you use Sacred Sword, and more power is just generally better!

In terms of problems, the biggest one I see is the lack of a Fighting resist. Something like a Scarf or CB Terrakion is going to get a kill every time it's in, and you can't switch Rotom in because CC will 2HKO it...and Scizor's defensive utility will fall apart if it gets hit by a CC. Bulk Up Conkeldurr has a ton of opportunities to set up with three choice users and the relatively harmless Ferrothorn, and if something like NP Lucario (with Vacuum Wave) gets to set up on locked-in Pursuit or Dark Pulse, it's going to get a clean sweep.

I would replace one of your choice users to solve this problem. Right now they're just giving set-up opportunities to Pokemon when you really can't afford it. You could also get rid of Infernape since designated leads are often a waste (especially if you opponent has a spinner...since you have no spinblocker for its SR or Ferro's Spikes :x). If you replace Hydreigon, Latios or Reuniclus are reasonable substitutes. Scizor has really good synergy with both of them so it might be worth a try, and they help with the Fighting-type weakness a bit. You'll still have so issues with CB Terrakion, but it's so strong that most teams do and you will probably only have to play around it a few times. Gengar is also a good option because it can *kind of* keep Terrakion in check, beats Conkeldurr with Disable, outspeeds Lucario and is immune to all of its priority except Bullet Punch, and serves as a spinblocker against anything but Starmie, and Infernape and Ferro are virtually useless against stall teams without spinblocker support...otherwise Ape just dies and Ferro is hazard set-up bait, Thunder Wave or not. If you opt to replace Infernape, I would put Stealth rock over Spikes on Ferrothorn and put in a really stable Fighting resist. The ones above work. Slowbro is also a decent option. It can help spread paralysis and blocks a lot of Fiighting-types (and is good backup for Gyarados!)...but I would just use an attacker since they fit with the offensive style of the team better.

Rain doesn't appear to be too much of a problem! Toxicroak is going to be a major issue, but IDK, it doesn't look too bad against Rain to me! I would suggest making Rotom more defensive to make it last longer (as I'd imagine your problem is that your Water resists are all easily worn down except for Ferro), but then you lose TrickScarf which is one of your only good weapons against stall. If you're really worried about it, you could replace Hydreigon with a Latios or Latias which both sponge Water hits (and even weaker Ice Beams) pretty well. I hate to mess with your MVP but it does contribute to just about all of your weaknesses :x

Lastly, I would try to focus a bit more on beating stall. Scizor and Rotom's Trick are good weapons and Terrakion is *deadly*, but it's a tad thin. Reuniclus (Calm Mind, to be specific) not only helps with Fighting-types but also is a pretty solid stallbreaker once you eliminate their "anti win condition" Pokemon (and anything with Taunt). Scizor can help do that.

I guess if I were to use the team myself, I would definitely replace Infernape with Calm Mind Reuniclus, put Stealth Rock over Spikes on Ferrothorn, and then maybe mess with the Hydreigon slot to see what you can come up with. Basically anything that has some utility against rain and backs up Reuniclus against Fighting-types would be welcome, and I would personally try out Gengar because it has stallbreaking potential, can set up on choiced Fighting-types, and has a field day if the opposing special wall can be Pursuited or TrickScarfed. Sorry for replacing Hydreigon, he's really cool I know :(

But yes, good luck and hopefully these suggestions were helpful.

The only change I'd like to make here is with Ferrothorn. Gyro Ball doesn't have good synergy with Thunder Wave, since paralysis weakens Gyro Ball's power (by cutting the opponent's Speed). Use Power Whip so Ferrothorn can readily threaten Water Pokemon while still hitting Terrakion hard.