Earthquake is an obligatory STAB move required to hurt switch-ins.

Slack Off is necessary to keep Hippowdon as healthy as possible to switch into attacks. This is particularly important, as Hippowdon will usually move second and needs the HP to avoid being 2HKOed.

Ice Fang is a solid coverage option that allows Hippowdon to break Substitute from Mega Salamence, Landorus-T, and other Pokemon immune to Earthquake.

Yawn allows Hippowdon to apply pressure and often forces switches. Stealth Rock is used for overall support, breaking Focus Sash and dealing great chip damage in general, especially to Pokemon weak to Rock.

If using Stealth Rock, use Whirlwind with it. The use of either Ice Fang or Whirlwind is obligatory for this set to actually check the likes of Substitute Mega Salamence and Landorus-T.

Rocky Helmet is the ideal item, dealing chip damage to physical attackers that make contact. It is particularly important because it actually allows Hippowdon to beat strong physical attackers like Mega Salamence and Mega Kangaskhan that could otherwise boost past Hippowdon.

Figy Berry can be a viable alternative if you are willing to give up these advantages for a quick health gain.

The given EV spread and nature are ideal for a physically defensive wall, making Hippowdon able to sponge as many physical hits as possible.

Sand Stream deals chip damage and disrupts opposing weather.

Hippowdon should stay in the back, only switching into physical attackers that cannot break through its massive bulk.

Use Slack Off to keep Hippowdon healthy enough to take two hits on the switch. Hippowdon will nearly always move last, and it is important to stay healthy enough to take hits.

However, be careful of using Slack Off too predictably against setup sweepers or when strong attackers like Greninja can come in freely.

Yawn forces switches and can deny momentum to otherwise safe switch-ins such as Gyarados.

Use Earthquake to limit Pokemon like Tapu Fini and Greninja from switching in.

Watch out for lures such as Metagross with Grass Knot designed to circumvent Hippowdon's massive Defense.

Hippowdon can concede free turns to Pokemon like Tapu Fini and Greninja. Use a partner such as Snorlax and Ferrothorn in order to absorb special attacks.

Frail hit-and-run attackers like Mega Charizard Y and Tapu Lele appreciate Hippowdon's ability to sponge hits from strong attackers. Mega Charizard Y also appreciates the weather reset from Hippowdon.

Yawn synergizes well with setup sweepers such as Mega Salamence and Mega Charizard X.

Yawn in combination with Stealth Rock applies a lot of pressure, earning free turns by forcing an opposing Pokemon to fall asleep unless the opponent has a way to absorb sleep using a Pokemon like Tapu Fini, Tapu Koko, or Gliscor.

Stealth Rock breaks Focus Sash to facilitate sweepers.

Earthquake is an obligatory STAB move required to threaten Pokemon neutral to Ground-type moves, particularly Greninja and Tapu Fini.

Whirlwind is the safest option to deny any potential setup with Substitute.

It is possible to use Slack Off instead of Whirlwind for longevity. However, this will leave Hippowdon prone to certain setup Pokemon such as Substitute Salamence and Landorus-T that it should be able to handle. Slack Off works better when Hippowdon has more Defense investment because specially defensive Hippowdon has a harder time finding targets to comfortably use Slack Off against.

An EV spread of 252 HP / 4 Def / 252 SpD with a Careful nature and Sitrus Berry allows Hippowdon to avoid a 2HKO from the biggest range of damage. Because its ideal scenario is to go for Stealth Rock and Yawn, two turns is all it needs to achieve its goal.

Figy Berry allows Hippowdon to take strong Z-Moves and heal back up to high HP, giving Hippowdon a chance to Yawn.

An EV spread of 228 HP / 140 + Def / 140 SpD allows Hippowdon to survive physical attacks like +2 Let's Snuggle Forever from Adamant Mimikyu while still having a good chance to survive a Devastating Drake from Naganadel, a big threat to the classic Hippowdon + Salamence core. As this spread aims to avoid OHKOs from Z-Moves, this and other mixed bulk spreads gain significantly more from Figy Berry as opposed to Sitrus Berry.

Sand Stream deals chip damage and disrupts opposing weather.

This type of Hippowdon is highly threatening if it gets a good lead matchup. Even if your opponent switches in a Pokemon that can 2HKO Hippowdon, it will have already set up Stealth Rock and started using Yawn. However, be aware that most opponents will lead with a Pokemon with a good matchup against Hippowdon because it is so threatening to give it a free turn.

If Hippowdon does end up getting an advantageous lead, it is possible for it to use Stealth Rock and Yawn repeatedly until something has to be put to sleep to KO it, which is a great time to switch into your setup sweeper.

Punish Tapu Fini switching in by using Earthquake.

If your opponent is unable to threaten Hippowdon, set up Stealth Rock first and then Yawn to guarantee that a foe falls asleep. However, using Yawn first is advisable if the opponent is able to take advantage of the first free turn given as Hippowdon sets up. Yawn will force the opposing Pokemon to fall asleep or switch out, giving Hippowdon a safe opportunity to set up Stealth Rock.

Consider leaving Hippowdon on the bench for matchups where it will have difficulties putting an opposing Pokemon to sleep.

Pair Hippowdon with strong setup Pokemon such as Mega Salamence, Mega Charizard X, and Mega Lucario, as they can take advantage of free turns gained by Hippowdon.

Have multiple Pokemon that are able to threaten the Water-types that counter Hippowdon, such as Tapu Koko and Choice Scarf Kartana.