Dynamax is banned in Gen 8 Monotype, so you'd need to use Weak Armor on Omastar. The Shuckle set is really bad, use hazard setter because it's the only good one. Also, it's better to invest in HP rather than both defenses because Shuckle's HP is very low.
Shuckle @ Mental Herb / Custap Berry
Ability: Sturdy
EVs: 248 HP / 252 Def / 8 SpD
Bold Nature
- Stealth Rock
- Sticky Web
- Knock Off / Toxic / Final Gambit
- Encore
First two moves are hazards, Knock Off and Toxic are for utility. Final Gambit allows you to get Shuckle out of the battle so that you can send your next Pokemon. Mental Herb is for Taunt, while Custap one-times allow you to move first at low HP.
Omastar is literally on the bottom of viability ranking at C, use Nihilego which can do the same thing specially but can snowball faster. I'd use Omastar if this was a Rain team, so even with the Spe boost from Shell Smash it's still pretty easy to revenge kill due to no Swift Swim.
Nihilego @ Power Herb
Ability: Beast Boost
EVs: 252 SpA / 4 SpD / 252 Spe
Timid Nature
IVs: 0 Atk
- Meteor Beam
- Sludge Wave
- Grass Knot
- Thunderbolt
Meteor Beam and Sludge Wave are STAB, while the latter two are coverage for Ground-types and Water-types.
Carbink is terrible, it's not even ranked. I'd suggest to also remove Gigalith, as you don't have a Sand abuser. Cradily can deal with Water-types so it's cool. Likewise, Coalossal makes up for Steel-type weakness and provides with hazard control (you lack Defog) as well as racking up chip damage with Spikes.
Coalossal @ Heavy-Duty Boots
Ability: Flame Body
EVs: 252 HP / 252 Def / 4 SpD
Bold Nature
IVs: 0 Atk
- Flamethrower
- Rapid Spin
- Scorching Sands
- Spikes
This team really lacks any speed control out of the Shell Smashers which is quite important, so I'd say you could use a Terrakion / Lycanroc-Dusk instead of Barbaracle, preferably one with Scarf for revenge killing.
Terrakion @ Choice Scarf
Ability: Justified
EVs: 252 Atk / 4 SpD / 252 Spe
Jolly Nature
- Stone Edge
- Close Combat
- Earthquake
- Poison Jab
TTar can also run Choice Band for extra power, and I'd say that's better than Dragon Dance but both are good.
Weakness Policy TTar can also, be fulfilled by Rhyperior thanks to Solid Rock.
Rhyperior @ Weakness Policy
Ability: Solid Rock
EVs: 252 HP / 4 Atk / 252 Def
Impish Nature
- Earthquake
- Fire Punch
- Ice Punch
- Stone Edge / Rock Slide
The bulk allows it to also act as a bulky attacker. Earthquake and Stone Edge are STABs, with Rock Slide being an option for those who prefer accuracy. Meanwhile, the elemental punches cover Grass-types as well as Corviknight who's pretty troublesome for any Rock-monotype.
Pokepaste
Sorry for changing most of your team, but it's because most of them aren't ranked in the viability rankings. Hope I could help :)
