In a nutshell: Ground
Just like how fireproofing a building is a necessity, so is protecting it against Ground-type moves. This is far easier, at least: many moves actually involve creating shockwaves that simulate localized quakes or creating dirt, earth, etc. The former can still be destructive (and highly accurate!), so upper floors especially need to be able to take these moves.
Pokemon of this type tend to be made up of softer materials than Rock-types. Because of their non-conductive skin, they are usually immune to Electric-type moves, but drenching them or somehow hitting the Pokemon's insides can work.
Who's who of type experts 1: Takashi "Giovanni" Sakaki
Born as the heir of the yakuza organization Team Rocket, young Takashi Sakaki was groomed from birth to take over the organization from his mother. She went as far to include the kanji for ambition in his name. However, he was disgusted by them and choose to strike out on his own as a Pokemon Trainer with his trusty Rhyhorn. It was something he excelled at, and he enjoyed the thrill of battle. He won badges from all across the world and even won a Championship – turning it down because he felt the position wasn't for him. He is much more commonly known as Giovanni, an he invented to distance himself from his family.
He eventually found a woman to settle down with, and needing an outlet for his battling itch, lobbied to become a Gym Leader which the Kanto League jumped on. Things were good for a while, he had a kid and everything, even got to choose his preferred type. He could've easily made Elite Four or Kanto League Champion if he felt compelled, and he almost did because of his son's expectations. But three things pushed him to take up his criminal birthright. The first was the unexpected passing of his wife in an accident. The second was boredom with testing trainers. Last was suffering a humiliating loss in a Gym Leader tournament – he needed more power, so he would take it. The rest is history.
He gained the support of three other Gym Leaders in the region – one willing, one not, and one somehow both at once. His plans got as far as taking control of the Silph Building in attempt to force them to produce a Master Ball. A certain scientist who was involved speculates this was to capture the original copy of Mew, which was sealed away in an unknown dungeon. In any case, the takeover failed due to the good half of Sabrina, the Officials being competent, and meddling kids. The team, while driven out of Kanto, remained active in the Sevii and Johto regions.
As far as the public knew, he was just the Gym Leader who was infrequently around. Even some of the team wasn't aware of his dual identity. The Officials didn't have enough evidence either, which is why they had to let him go when he disbanded the Team in shame after they were defeated. Some believe his attempted takeover of Kanto was a means of destroying the team. Whatever the case, he left to become a wandering trainer again to gain power his own way, going as far to attend some tournaments. Ironically, his own son was disgusted by him and set to walk a similar path of independence and Rocket-hating.
He has recently returned to leadership because what the remnants were turning his family business into utterly disgusted him, with plans to clean up the organization with the ultimate goal to turn it legit. Out-of-universe, because really, more people need to write post-RBY Gio rather than what the anime made him become in subsequent games, but I'm splitting the difference.
Who's who of type experts 2: Clay Castillo
A mountain of a man hailing from an American region where everything is bigger. Clay is the overseer of a mine in Unova, which is also the location of the Driftveil Gym (so he can handle both of his jobs at once). He relocated to there from his home region as part of a business venture. While he is technically the president of his own company, he often gets personally involved with the work with his Pokemon and his trusty pickax. He has very high standards for anything, although he has an appreciation for people who are both willing and able to follow their dreams. It's what he did, after all, going from rancher to miner.
Clay has many epithets: his official title of Underground Boss, the Miner King, the Dusty Cowboy, and a few others. He got his Gym Leader position when the incumbent Gym Leader of Driftveil stepped down to start a family, and suggested him as a replacement. While annoyed at first because he had one himself and never let that slow him, he eventually accepted at his workers' behest. Ironically, he rose to become the leader of the Unovan Gym Leaders due to his charisma and management skills. Whenever the League needs a representative, he's usually the one they send, especially if the Champion Alder isn't available and sometimes even when he is. People think he can become even better, but there's too much else in his life to focus entirely on Pokemon.
Clay also happens to be an automobile enthusiast. He formed an unlikely acquaintanceship with Volkner Denzi during a global Gym Leader meetup because of it. Though their tastes in vehicles differ, they both enjoy working on them in their spare time. One might expect him to be good friends with another Sinnoh Gym Leader, Byron Vass: also a father, leader, and Gym Leader involved in mining. However, Clay doesn't like the guy, for reasons both slightly sensible (seeing him as a business rival) and petty (disagreements with how Byron treats his family).
Pokemon commentary 1: Infused into earth
There are a number of Pokemon who appear to be permanently attached to the ground beneath them. Many of these are Ground-types, with Diglett being the most famous example. It's believed these are so attuned with their type that they stay in contact at all times. In all cases, they move by "gliding" along the ground (to the relief of building designers everywhere), not disrupting it unless they use Dig. Uneven surfaces and tough material seem to slow them anyway, however. These Pokemon go as far as pulling part of the ground with them when thrown or when using a move that elevates them (most need indirect means like Mimic). They even take some into their Poke Balls, making use of it in case they are sent out in midair. Because of this, some theorize that their burrow is part of these Pokemon's bodies, but the exact nature is under investigation.
It's always been known what they look like below, by the way. X-rays, predators, and the Pokemon themselves have confirmed their appearance. They give no indication as to why these Pokemon are the way they are.
Pokemon commentary 2: Golett and Golurk
Although the modern relationship between humanity and Pokemon goes back 1500 years, the two species were interacting long before that. These two Pokemon are such an example.
Rumors surround these Pokemon, wildly speculating that they were created by aliens, an advanced ancient civilization, or even came from the future. There is absolutely no evidence of any of that. What is a fact is that they are partly manmade Pokemon, sculpted from clay and earth, and that remains of them date back 3000 years. The most commonly accepted theory is that they are the spirits of fallen Pokemon given new bodies in exchange for performing labor, fused through an ancient ritual. They came to change over the ages after Dittos helped propagate their numbers, becoming more robot-like internally.
They are very faithful to the cause they serve. They silently carry out their orders, unable to speak yet able to understand others even beyond what all Pokemon are capable of. However, some seem to have what appear to be programming faults (for lack of a better term). Around half have difficulty handling small objects, and rarely one will disregard its own safety when attacking. Since it's unlikely that they would have intentionally been given these abilities, it's believed they developed over time.
Menacing moves:
• Magnitude: One of many moves that simulates localized seismic activity, as mentioned above. They're very effective on things in the ground, but won't affect things that aren't on it. This version is wild and quick, but very unreliable for it.
• Mud moves: While these are best used by Pokemon that can use Ground and Water attacks, a special TM let just about any Pokemon learn how to throw a Mud-Slap with whatever dirt is on the ground. They are good examples of Ground-type moves that can hit things that fly.
• Dig: While the property damage from using this move on a floor is less than you'd expect (the tunnels they burrow fill in behind them), most battlefields you see will be made of dirt, grass, or other easily replaceable materials to minimize what needs to be done. A well-trained Pokemon can take their trainer right out of a cave with this.
• Scorching Sands: A move innovated by humanity. The creator actually expected this blasting of heated sand to turn out to be a Fire-type move. It can be used creatively on things like Sand Tomb.
• Earth Power: By focusing their essence, this move causes a blast of pure Ground-type energy to erupt from the desired location.
Noteworthy Pokemon in-fic: Various Rhyhorns and Rhydons
During his initial training with the Demon, Nori Carino encountered a mother Rhydon on Route 214. It proved a powerful and worthy opponent for the Demon, and unbeknownst to Nori, the Rhydon recognized the o'Fyma. It was with Nori's advice to go for the legs that the Demon was first able to gain ground. They ultimately defeated her, and Nori realized the Demon wasn't so bad when she spared severely harming the Rhydon and seemed to urge it to stop fighting for its child's sake. A Rhyhorn got an off-hand mention as one of the opponents Nori had Pachi defeat during a bit of training.
And in Abyssal Despair, a member of Nori's middle school battling team, Emi Pikaru challenges him with a Rhydon. It brings back memories. Despite being exceptionally well trained, able to use Thunder to empower himself (or hit opponents at weird angles by deflecting it) and even use Water Gun alongside moves you'd expect, he falls to the Demon's superior level of power and combat experience.
