Okay, let’s go through this.
Grimmsnarl
Good job, this was a fine set.
Toxapex
Don’t use Liquidon, it’s completely useless on Toxapex, replace it with Scald otherwise its a nice set. Evs Spread could be 252 Hp / 60 Def / 196 SpD calm nature will be better in my opinion seems it could at least get some chance to not be OHKO from one of it’s biggest “Predator” — Magnezone.
252+ SpA Choice Specs Magnezone Thunderbolt vs. 252 HP / 4 SpD Toxapex: 356-422 (117.1 - 138.8%) -- guaranteed OHKO
Possible damage amounts: (356, 362, 366, 372, 374, 378, 384, 386, 392, 396, 398, 404, 408, 414, 416, 422)
252+ SpA Choice Specs Magnezone Thunderbolt vs. 252 HP / 196+ SpD Toxapex: 284-336 (93.4 - 110.5%) -- 56.3% chance to OHKO
Ferrothorn
Looks fine but the 30 Speed IVs mean nothing, 0 Speed Ivs will do better. And also, I suggest you to use Gyro Ball due to that it’s painful low speed.
Hydreigon
Uh-oh... a same type pokemon in one team wasn’t too good, it type was same as Dragapult (Which could do better job than it ) and Grimmsnarl, and I don’t think it was a good idea.
But however, Wide Glasses wasn’t a good Item for it, Choice Spes was much more reliable than Wide Glasses on it if you want a Special Wallbreaker and I highly suggest use Draco Meteor than Dragapult. 130 x 1.5 + 75 x 1.5 (after the stat lost but boost a bit by Choice Spes) = 307.5 bp 85 x 1.5 x 2 = 225. As you may see, a draco meteor could hit much more power than Dragon pulse, so you should change it. And, Nasty Plot change to Flamethower / Fire Blast / Earth Power for coverage and it’s fine power, or you may use U-Turn for enmergancy.
Again, if you want a wall breaker, in this site, it might will give you more guide and remember don’t choose the same type with one of your pokemon in your team if you can!
Dragapult
Looks fine.
Toxtricity
Two wallbreakers? Umm...not a good idea but I think it was still acceptable. The only thing that I want to change was Shift Gear, the only thing it can boost was speed. But, however Nuzzle could be a better choice seems it will cut opponent speed to half and make opponent 30 % chance cant move, and it also got 20 power and 100 acc which means it was a pretty good choice for it.
These are my suggestion, hope it helps! (and p.s., click the Green Checkmark on the right top of my answer if you think it really helps you, thanks!)