Rockium Z (and other items)



Gigalith @ Rockium Z  / Groundium Z / Weakness Policy
Ability: Sand Stream  
Level: 50  
EVs: 212 HP / 116 Atk / 180 SpD  
Brave Nature  
IVs: 0 Spe  
- Stone Edge / Rock Slide  
- Earthquake  
- Wide Guard / Heavy Slam
- Protect

Milestones:
- Has a 3.5% chance of being 2HKOed by Timid Life Orb Tapu Koko's Thunderbolt
- Tapu Lele's Z-Psychic has a 12.5% chance to OHKO Gigalith in sand.
- Can potentially OHKO 252 HP Arcanine, Alolan Marowak, and Araquanid with Stone Edge. 

As mentioned, Gigaliths high defensive stats and usable coverage moves makes itself a potent bulky offensive Pokemon in the format. Rockium Z is a popular item and Z-move choice that allows Gigalith to inflict massive Rock-type damage against a target who doesn't appreciate it like Fire-, Flying-, Bug-, or Ice-type Pokemon. Despite the shacky accuracy and power point value, some Gigalith base their Continental Crush on the Rock-type Stone Edge for a whopping 180 base damage before STAB. If Stone Edge isn't as good option, Rock Slide is slightly more accurate with high Power Points, yet its Z-Move will be signifcantly lowered to 140 base damage instead. To round off its coverage, Earthquake is a staple strong Ground-type move to hit the ever common Electric-, Steel-, Fire-, Poison-, and opposing Rock-types Pokemon. 

Most options for Gigalith usually deviate from here given the team compositions and what best suits the Rock-type. Wide Guard is a good support move to block spread damage like Earthquake or Discharge from harming its allies. Heavy Slam is a decently strong coverage option notably used against Fairy-type Pokemon such as Tapu Lele, Mimikyu, and Alolan Ninetales who don't appreciate a base 120 Steel-type move. Groundium Z can be used to lure potential ground-weak Pokemon such as Alolan  Muk or Tapu Koko and potentially OHKO them in one hit. Lastly, Weakness Policy is an interesting item choice which give Gigalith +2 Attack, but needs to be hit with a super effective move, so timing and potentially self damage is key. 

For a list of damage calculations for this Magnezone set, see below for offensive calcs. 

Offensive Calcs

Curse Setup

Gigalith @ Rockium Z / Figy Berry
Ability: Sand Stream  
Level: 50  
EVs: 244 HP / 84 Atk / 180 SpD  
Brave Nature  
IVs: 0 Spe  
- Stone Edge / Rock Slide  
- Earthquake  
- Curse  
- Protect

Milestones:
- OHKOs up to228 HP / 116 Def Celesteela with +1 Z-Stone Edge after a boosted Curse.
- Withstands two Earthquakes from Garchomp with +1 defense boost.
- Withstands Z-Psychic from Tapu Lele with sand.
- Takes two Life Orb Timid Tapu Koko's Thunderbolt.
-Takes less hail damage due to HP value. 

Even with an impressively high base 135 attack and 130 defense stat, Gigalith has access to the move Curse which can bolster these two stats to formidable heights. Unlike most Curse user like Snorlax or Alolan Muk who have somewhat respectable attack stats, Gigalith already a higher attack and better defense on both ends to start out with and can become an immediate threat to the opponent with one Curse boost. Likewise, make sure to have a Trick Room option for Gigalith to ensure it can outspeed its opponents its lackluster speed, and pick off any target with with Rock- and Ground-type coverage. For Rock-type coverage, Stone Edge is preferred for a couple of reasons given Gigalith has a stronger base Z-move with it than Rock Slide and doesn't get blocked by Wide Guard. Rock Slide is a decent alternative for more Power Points and the flinch option (in Trick Room), however note Z-Rock Slide is much less powerful and a Wide Guard user can potentially block this set. Earthquake is Gigalith's main response to any Fire-, Steel-, Poison-, and Rock-type Pokemon on the field. In fact, a +1 Earthquake from this set has a 100% chance to OHKO 4 HP Tapu Koko and 2HKO other Gigalith. For item choice, it comes down to whether the user wants a one-time nuke in Z-Stone Edge / Z-Rock Slide likely coming from a boosted Curse, or if HP replenishment and more setup chances from Figy Berry or other 50% berries is preferred. 

Assault Vest

Gigalith @ Assault Vest  
Ability: Sand Stream  
Level: 50  
EVs: 244 HP / 196 Atk / 52 Def / 16 SpD  
Brave Nature  
IVs: 0 Spe  
- Rock Slide  
- Earthquake  
- Heavy Slam  
- Stone Edge / Bulldoze

 

Milestones:
- Withstands 2 boosted Life Orb Psychic and Thunderbolt from Tapu Lele and Tapu Koko respectively. 
- OHKOs up to 164 HP / 92 Def Tapu Lele with Heavy Slam.
- Has a 0.4% chance to be 2HKO by Magnezone's Flash Cannon. 
- OHKOs 252 HP Arcanine, Alolan Marowak, and Araquanid with Stone Edge. 
- Takes two Boomerangs from Alolan Marowak.
- Has a 1/8th chance being OHKOed by Araquanid's Liquidation. 

Gigalith is one of the few Pokemon in the format who benefits greatly with the Assault Vest given it has a workable coverage options and few necessary status moves aside Protect or Wide Guard. With the raised special defense stat thanks to the sandstorm it brings, Gigalith's special defense stat reaches at about over 200 (223 for this set) and is capable of withstanding some of the strongest special attacks in the format. Two examples of these incredible feats include Gigalith withstanding two Life Orb Psychic from the common Tapu Lele or Thunderbolt from Tapu Koko in their respective terrain and with the chance to OHKO them afterward. With the Assault Vest, Gigalith can be used as a decent check to many special attackers in the format who aren't able to OHKO it back immediately such as Tapu Lele, Tapu Koko, Nihilego, Porygon-Z, etc. For coverage, Rock Slide is listed to deal spread damage against foes and can flinch targets down, assuming Gigalith is under Trick Room. Earthquake inflicts super effective damage against Fire-, Electric-, Steel-, and Rock-type Pokemon who are common such as Arcanine, Tapu Koko, Nihilego, Metagross. Heavy Slam is decent Steel-type coverage to potentially OHKO most Fairy-type Pokemon like Tapu Lele, Mimikyu, Comfey, etc especially given Gigalith's weight. Stone Edge is a secondary Rock-type STAB which can deal better than than Rock-type against super effective targets with a high crit chance, but has flimsy accuracy. Lastly, Bulldoze is an option in case Gigalith's team needs speed control of sorts by lower the speed of the targets by one stage.