It seems that every other generation we get a spiritual successor to Rhydon in that it has excellent HP, attack, and defense and is typically a Rock type. We have Rhydon, Tyranitar, Aggron, Coalossal, and of course Gigalith. One of Cheren's offensive aces and every Rock collector's dream, Gigalith got a boost in gen 7 when it got access to the previously rare Sand Stream ability, however Gigalith has otherwise remained pretty unchanged since its introduction in gen 5. It hits hard, can take hits, but is incredibly slow and has no access to reliable recovery. If there was a means to rectify those last two issues Gigalith probably would be more widely used, but sadly Gigalith just lacks that extra "oomf" that the previous Rhydon clones have. It can't run an Eviolite set like Rhydon, Be the tanky powerhouse that is Tyranitar, wreck opposition like no recoil Head Smash Aggron, or Rapid Spin like Coalos...on second thought don't use Coalossal. Just don't. Instead, let's just focus on this crystal crusher.
Cursed Gemstone
Ability: Sand Stream
Item: Leftovers
Nature: Careful (+Sp.Def -Sp.Att)
EVs: (HP 252) (Def 4) (Sp. Def 252)
Moves:
Curse
Stone Edge/Rock Slide
Earthquake
Body Press/Stealth Rock/Gravity/Rest
Set Details:
Set up Curse to increase offensive output and defensive bulk at the cost of an inconsequential speed drop, Stone Edge will be your main STAB but Rock Slide is a good alternative if the low PP is a turn off, and Earthquake synergizes well with your Rock STAB. The last slot is a toss up depending on your preference. Body Press is good Ferrothron repellent and fills any holes that Rock and Ground do not cover, Stealth Rock is always a good option so the opposition feels the entry damage long after Gigalith is gone, Gravity pairs well with Stone Edge and Earthquake since it makes the former 100% accurate and the latter able to hit Flying types and Levitators, and Rest is your only recovery option if you are truly invested in keeping Gigalith around longer. Ability goes to Sand Stream since it serves as a means to inflict residual damage and provide an extra 50% boost to its special defense when active, item obviously goes to Leftovers to make Gigalith last as long as possible, and nature and EVs are focused on HP and special bulk to shore up defenses in its weaker stat.
Assault Crystal
Ability: Sand Stream
Item: Assault Vest
Nature: Adamant (+Attack -Sp.Att)
EVs: (HP 252) (Attack 252) (Sp. Def)
Moves:
Stone Edge
Earthquake
Body Press/Superpower
Iron Head/Throat Chop/Explosion
Set Details:
Now to focus a set that's more offense and less set up. Assault Vest shores up Gigalith's special defense which in tangent with Sandstorm allows it to take special attack incredibly well. In an all-out offensive assault we obviously have Stone Edge and Earthquake in prefect harmony, Body Press or Superpower handles Ferrothron and most threats that can take the Rock/Ground combo, and the last move is your choice of coverage. Iron Head punishes the Fairy types, Throat Chop gives Psychic and Ghost types a nasty surprise, or you could just kamikaze yourself with Explosion if you want to throw reckless abandon at your opponent. Nature and EVs this time are focused on HP and Attack.