What to use:
Hippowdon (M) @ Leftovers
Trait: Sand Stream / Sand Force
EVs: 252 HP / 244 Def / 12 SDef
Impish Nature (+Def, -SAtk)
- Earthquake
- Slack Off
- Stealth Rock / Whirlwind
- Ice Fang / Whirlwind
Role: Physical Wall
What it does: Let's talk about what Hippowdon has over other physical walls. The first thing that people think when thinking of a physical wall is Skarmory. However, Hippowdon is just as good. It actually has more physical bulk than Skarmory, and only faces competition because the latter is a Steel-type and has Spikes. But Hippowdon's higher physical bulk allows him to counter things that Skarmory cannot, such as Terrakion. Hippowdon also faces competition from Landorus-T. However, it has two things that separate him from the flying tiger. Landorus-T whishes that it had reliable recovery, and acess to phazing. These are things that Hippowdon does have, and thus, it is not outclassed.
Well, let's talk now about Hippowdon itself. Apart from the high defenses, Hippowdon has a good Attack, which means that it hit rather hard for a defensive Pokémon. Thus, it is not setup bait unless the opponent is immune or resistant to the attacks that Hippowdon may use.
Earthquake is the main STAB move. With this move, Hippowdon does not become setup bait for things with Taunt. It also lets him OHKO things like Terrakion, which makes him one of Terrakion's best counters. Slack Off is a reliable recovery move that extends Hippowdon's longevity, letting him survive to more physical assaults. This separates him from Landorus-T, which will fall to repeated hits. Stealth Rock is a move that Hippowdon can reliably setup on the face of many physical threats. Ice Fang has great coverage with Earthquake, and lets it hit Dragon-types that are immune to Earthquake, such as Dragonite. Hippowdon is one of the few non-Steel-types capable of surviving boosted Dragon-type attacks, and with Ice Fang, it can survive one Outrage and OHKO back. Either Stealth Rock or Ice Fang can be replaced by Whirlwind. Whirlwind is a great move to phaze problematic threats that you cannot defeat with either Earthquake or Ice Fang. It also breaks Baton Pass chains without being disrupted by Mr. Mime, and surprises opponents expecting to use Hippowdon as setup fodder.
The ability is up to you. Hippowdon has Sand Stream, and it is a reliable sandstorm inducer instead of Tyranitar, thanks to its greater survivability in general. It is also the only weather inducer with reliable recovery, thus, Hippowdon is the weather inducer that tends to survive more. Keep in mind that Hippowdon lacks the same Special Defense and the same offensive prowess of Tyranitar, and thus, do not expect him to defeat the same threats as Tyranitar, or to not be setup fodder for certain Pokémon. If you have the intention of using Hippowdon has a physical wall on a rain or sun team, don't worry: Hippowdon can use Sand Force, which keeps him from interfering with the weather. Although it seems like at this point you would be better off with Landorus-T, remember that Landorus-T lacks phazing and reliable recovery. Thus, do not shy away from trying to use Hippowdon.
Good Teammates: Skarmory is actually a great partner for Hippowdon. Despite Hippowdon's great physical bulk, it will fall to repeated Dragon-type assaults. This is not to mention that Hippowdon cannot counter certain physically based threats, like Breloom or Gyarados. Due to its Steel/Flying typing, Skarmory can wall those threats, and can phaze them. It also has access to Spikes, which complets with Hippowdon's Stealth Rock to rack up more hazard damage. In return, Hippowdon protects Skarmory from threats like Terrakion, non-CB Victini, and the rare Gravity Landorus. Thus, despite seemingly redundant, Skarmory is a great physical wall to use alongside physically defensive Hippowdon: thogether, they will certainly protect you from almost any physical sweeper.
Apart from Skarmory, there are other walls that can be used as partners. Specially defensive Celebi is one of them. Celebi protects Hippowdon from specially based threats like Sheer Force Landorus. SpD Jirachi also does the same and has access to Wish to support the rest of the team. Chansey and Blissey are other special walls that can be paired with Hippowdon. The problem is that both are prone to become setup bait unlike Celebi and Jirachi. They also have problems walling certain physically based threats, as well as Keldeo, the only special attacker that can entirely bypass them. A spinner is recommended to get rid of Toxic Spikes, which will render Hippowdon useless. Sadly, the only spinner that tends to be good alongside Hippowdon, is Tentacruel. Xatu can also be used. It is not a spinner but can reflect hazards with its ability Magic Bounce.
On the topic of sandstorm partners, Terrakion is one of the best, as it benefits from the sand to have a 50% boost to its Special Defense. Hippowdon can take assaults from certain things that trouble Terrakion, like Scizor, but be very wary of offensive Swords Dance sets from Scizor, which can 2HKO Hippowdon without a second thougth. Landorus is another potential partner, though Terrakion has better synergy with Hippowdon. Stoutland also benefits from the sand to become a great revenge killer and late-game sweeper under sand. In fact, the combination of Hippowdon and Stoutland is very common. Sadly, these are the only potential partners, as there are almost no Pokémon capable of abusing the sandstorm.
What Counters It: Xatu is the best counter to Hippowdon, as it is immune to Earthquake, doesn't care much about Ice Fang, reflects both Stealth Rock and Whirlwind, and can use Toxic to put a time on Hippowdon's like as Toxic cannot be stalled out by Slack Off. Anything that is immune or resistant to Earthquake and packs a powerful special attack is a counter to Hippowdon. Latios, Thundurus-T (with Grass Knot), and offensive Celebi are some examples. Hippowdon has a bad special bulk, thus, it will fall to most powerful special hits, even if they aren's super-effective. Hippowdon also fears Kyurem and bulky-Water types, all whick will force him out as they pack super-effective attacks against Hippowdon. There are also some physical attackers that even Hippowdon fears. These include Breloom and Gyarados, as they have super-effective attacks against Hippowdon. Lastly, anything immune to Earthquake and that packs Taunt is capable of stopping Hippowdon on its tracks. Air Balloon Heatran is an example. However, Balloon Heatran must avoid Ice Fang, as it will pop the ballon, and Hippowdon can then OHKO back with Earthquake.