I started with Mega Diancie, the greatest Pokemon on Rock. It's just a really fast and strong special attacker that can also bounce back hazards and status with Magic Bounce. I went with a Calm Mind set to further increase its wallbreaking potential.
After that I put Shuckle on the team with its access to Stealth Rock+Sticky Web and generally being an awesome utility Pokemon.
As with my previous Rock RMT, I went with Scarf Terrakion+Band Tyranitar as an amazing offensive core alongside Mega Diancie. Scarf Terrakion does a nice job of beating Scarfers like Hydreigon and Kyurem-Black that can threaten Mega Diancie, and Band Tyranitar does a great job breaking through balance teams like Psychic and Poison.
Every Rock team needs a Mega Scizor check, and for this team, I went with Alolan Golem over Rhyperior thanks to being able to further improve the Steel matchup, as well as the Fairy and Grass matchups thanks to Magnet Pull.
For the final Pokemon, I went with Cradily, who offered a nice Water immunity as well as a good switch-in against Scarfers like Landorus-Therian and Garchomp. It can also surprise special attackers with Mirror Coat if needed.
Now let's take a look at the Mountaineers!
Golem-Alola @ Firium Z
Ability: Magnet Pull
EVs: 128 Atk / 136 SpA / 244 Spe
Naughty Nature
Alolan Golem fills the essential role as the team's primary Mega Scizor check. As such, the 136 EVs in Special Attack allow it to guarantee the OHKO with Inferno Overdrive against defensive variants after Stealth Rock, and 244 Speed allows it to outspeed uninvested sets before they can U-turn. It also does a nice job of trapping and removing Ferrothorn in the Grass matchup, as well as Klefki in the Fairy matchup. In fact, Brick Break is used specifically to make sure that Klefki doesn't keep up screens when it goes down. Outside of that, Wild Charge is its best Electric STAB move, Earthquake is solid coverage, and Fire Blast is for hitting Mega Scizor as well as other targets like Ferrothorn.
Cradily @ Leftovers
Ability: Storm Drain
EVs: 208 HP / 252 Def / 48 Spe
Bold Nature
IVs: 0 Atk
Cradily fills the role as the Water immunity, Ground and Grass switch-in, and the best check the team has for opposing Mega Diancies. The 48 Speed is used to outspeed max Speed Azumarill after Sticky Web in order to KO it after it uses Belly Drum. Giga Drain is its best Grass STAB move, Toxic is nice for wearing down opposing walls, Recover is essential for sustain, and Mirror Coat is used to catch special attackers like the aforementioned Mega Diancie by surprise.
Shuckle @ Mental Herb
Ability: Sturdy
EVs: 248 HP / 252 Def / 8 SpD
Impish Nature
Shuckle serves the role as the team's hazard setter with both Stealth Rock and Sticky Web. It also offers important utility in Knock Off and Encore, with Knock Off being able to remove Chansey and Porygon2's Eviolites, as well as Choice Scarves from threats like Greninja and Landorus-Therian, and Encore being able to cripple setup sweepers and hazard setters. Additionally, it has extremely helpful neutralities to Grass, Fighting, and Ground, letting it absorb many hits before going down. The Mental Herb allows it to guarantee hazards against hyper offensive types like Fighting and Psychic.
Terrakion @ Choice Scarf
Ability: Justified
EVs: 252 Atk / 4 SpD / 252 Spe
Jolly Nature
Terrakion fills the role as the team's best revenge killer, being able to check Scarfers like Tapu Bulu, Hydreigon, Excadrill, and fast Pokemon in general like Tapu Koko and Mega Lopunny. With Sticky Web support, it's also able to outspeed weather sweepers like Excadrill and Kingdra, which are huge threats to any Rock team. Stone Edge and Close Combat are the basic STAB moves, Earthquake is important for hitting Tapu Koko and Nidoking, and Poison Jab is for hitting Tapu Bulu. However, Iron Head can be ran over it if you want to hit Mega Diancie.
Tyranitar @ Choice Band
Ability: Sand Stream
EVs: 12 HP / 252 Atk / 244 Spe
Adamant Nature
Tyranitar is the team's physical wallbreaker, used to tear through balance builds like Poison and Psychic. It also has Sand Stream to give everyone on the team a Special Defense increase. 244 Speed is used to outspeed Banded Victini after Sticky Web, as well as other base 100's like Mew and Volcarona. Stone Edge and Crunch are its best STAB moves, Fire Punch is great coverage for nailing Ferrothorn and Forretress, and Earthquake allows it to hit Toxapex and Tapu Koko.
Diancie-Mega @ Diancite
Ability: Clear Body
EVs: 252 SpA / 4 SpD / 252 Spe
Timid Nature
IVs: 0 Atk
Welp, I saved the best for last. Mega Diancie is the team's special sweeper/wallbreaker that is capable of completely running through types like Fighting, Dark, and Dragon. While 4 attacks is a more popular set for Mega Diancie, I decided to go with a Calm Mind set, allowing it to put in even more work against Water, Poison, Fairy, and Grass. Power Gem and Moonblast are the STAB moves of choice, and Earth Power is great coverage for hitting Heatran, Nidoking, and Toxapex. Hidden Power Fire is an alternate option for hitting Ferrothorn, but Alolan Golem already traps and removes it.
Here are some replays:
Vs Dragon:
http://replay.pokemonshowdown.com/gen7monotype-621743846
Vs Rock:
http://replay.pokemonshowdown.com/gen7monotype-623093882
Vs Dragon again:
http://replay.pokemonshowdown.com/gen7monotype-625228569
Vs Ghost:
http://replay.pokemonshowdown.com/gen7monotype-625257692
Vs Bug:
http://replay.pokemonshowdown.com/gen7monotype-625266468
Vs Normal:
http://replay.pokemonshowdown.com/gen7monotype-626044731
Vs Steel:
http://replay.pokemonshowdown.com/gen7monotype-626048096
Vs Flying:
http://replay.pokemonshowdown.com/gen7monotype-626050831
Vs Electric:
http://replay.pokemonshowdown.com/gen7monotype-626054149
Vs Water:
http://replay.pokemonshowdown.com/gen7monotype-626070714
Vs Dragon for the 3rd time:
http://replay.pokemonshowdown.com/gen7monotype-626077252
Vs Grass:
http://replay.pokemonshowdown.com/gen7monotype-616665426
Vs Ground:
http://replay.pokemonshowdown.com/gen7monotype-616681560
http://replay.pokemonshowdown.com/gen7monotype-621743846
Vs Rock:
http://replay.pokemonshowdown.com/gen7monotype-623093882
Vs Dragon again:
http://replay.pokemonshowdown.com/gen7monotype-625228569
Vs Ghost:
http://replay.pokemonshowdown.com/gen7monotype-625257692
Vs Bug:
http://replay.pokemonshowdown.com/gen7monotype-625266468
Vs Normal:
http://replay.pokemonshowdown.com/gen7monotype-626044731
Vs Steel:
http://replay.pokemonshowdown.com/gen7monotype-626048096
Vs Flying:
http://replay.pokemonshowdown.com/gen7monotype-626050831
Vs Electric:
http://replay.pokemonshowdown.com/gen7monotype-626054149
Vs Water:
http://replay.pokemonshowdown.com/gen7monotype-626070714
Vs Dragon for the 3rd time:
http://replay.pokemonshowdown.com/gen7monotype-626077252
Vs Grass:
http://replay.pokemonshowdown.com/gen7monotype-616665426
Vs Ground:
http://replay.pokemonshowdown.com/gen7monotype-616681560
So that was Mountaineers: The Offensive Rock Team! I really hope you enjoyed it, and if you want to use it yourself, here it is:
Golem-Alola @ Firium Z
Ability: Magnet Pull
EVs: 128 Atk / 136 SpA / 244 Spe
Naughty Nature
- Wild Charge
- Earthquake
- Fire Blast
- Brick Break
Cradily @ Leftovers
Ability: Storm Drain
EVs: 208 HP / 252 Def / 48 Spe
Bold Nature
IVs: 0 Atk
- Giga Drain
- Toxic
- Recover
- Mirror Coat
Shuckle @ Mental Herb
Ability: Sturdy
EVs: 248 HP / 252 Def / 8 SpD
Impish Nature
- Stealth Rock
- Sticky Web
- Knock Off
- Encore
Terrakion @ Choice Scarf
Ability: Justified
EVs: 252 Atk / 4 SpD / 252 Spe
Jolly Nature
- Stone Edge
- Close Combat
- Earthquake
- Poison Jab
Tyranitar @ Choice Band
Ability: Sand Stream
EVs: 12 HP / 252 Atk / 244 Spe
Adamant Nature
- Stone Edge
- Crunch
- Fire Punch
- Earthquake
Diancie-Mega @ Diancite
Ability: Clear Body
EVs: 252 SpA / 4 SpD / 252 Spe
Timid Nature
IVs: 0 Atk
- Power Gem
- Moonblast
- Earth Power
- Calm Mind
Ability: Magnet Pull
EVs: 128 Atk / 136 SpA / 244 Spe
Naughty Nature
- Wild Charge
- Earthquake
- Fire Blast
- Brick Break
Cradily @ Leftovers
Ability: Storm Drain
EVs: 208 HP / 252 Def / 48 Spe
Bold Nature
IVs: 0 Atk
- Giga Drain
- Toxic
- Recover
- Mirror Coat
Shuckle @ Mental Herb
Ability: Sturdy
EVs: 248 HP / 252 Def / 8 SpD
Impish Nature
- Stealth Rock
- Sticky Web
- Knock Off
- Encore
Terrakion @ Choice Scarf
Ability: Justified
EVs: 252 Atk / 4 SpD / 252 Spe
Jolly Nature
- Stone Edge
- Close Combat
- Earthquake
- Poison Jab
Tyranitar @ Choice Band
Ability: Sand Stream
EVs: 12 HP / 252 Atk / 244 Spe
Adamant Nature
- Stone Edge
- Crunch
- Fire Punch
- Earthquake
Diancie-Mega @ Diancite
Ability: Clear Body
EVs: 252 SpA / 4 SpD / 252 Spe
Timid Nature
IVs: 0 Atk
- Power Gem
- Moonblast
- Earth Power
- Calm Mind
Shoutout to Moosical for the banner :)