How to Beat the Elite Four in Pokémon Sun and Moon

Have a good team of Pokémon. Preferably, you'll want a team of six Pokémon that all have different types, without overlapping any types. Unless you're doing a challenge run with unevolved Pokémon, they should all be fully evolved (though there are some Pokémon that don't have a pre-evolution or evolution). You should also pay attention to their movesets - for example, a Primarina with a moveset of Sparkling Aria, Ice Beam, Moonblast, and Psychic would be better than having a moveset with more than one Water and/or Fairy-type move. Held items can also help you - for example, having a Primarina hold Primarina Z will allow you to transform its Sparkling Aria into Oceanic Operetta, a super-powerful move that can deal a ton of damage!

Train your Pokémon. Your Pokémon should be at least level 55 before taking on the Elite Four for the first time. To make training faster, have the Exp. Share on, so that all your Pokémon gain experience in a battle. You should also play with your Pokémon in Pokémon Refresh, so that they'll gain boosted experience in battles.

Buy a supply of healing items and Revives. You'll want to buy Hyper Potions, Max Potions, Full Restores, and Revives. Keep in mind, Hyper Potions heal 120 HP, rather than the 200 HP it healed in previous Pokémon games. This will end up being expensive, so spend your money wisely. If you have any items that you can sell, such as Nuggets and Star Pieces, sell them, so that you'll have more money to spend.

Go to Mount Lanakila. From the Pokémon Center, go left, then up to reach the Pokémon League. It's a fairly long stretch, so you may want to consider using the Tauros Charge to reach it faster. The first time you go to Mount Lanakila, you'll be challenged by Hau, who has a team of Alola form Raichu, Jolteon/Flareon/Vaporeon (which one he uses depends on the starter you chose), Komala, and the fully evolved form of the starter whose type is weak to the one you chose (Incineroar, Primarina, or Decidueye). Beat him if you haven't already done so.

Go up to the guards. They will tell you that you can't leave after going inside the Pokémon League. They will then ask you if you accept that. Say yes, and the door to the Pokémon League will open. Go inside.

Know about the Elite Four. The four Elite Four members you'll be facing are Hala, Olivia, Acerola, and Kahili. The next four steps will detail them in that order, but you can choose the order you face them in.

Defeat Hala. He uses Fighting-type Pokémon. He has a level 54 Hariyama, level 54 Primeape, level 54 Bewear, level 54 Poliwrath, and level 55 Crabominable. Fighting types are weak to Fairy, Psychic, and Flying type moves. In addition, Bewear is weak to Fighting type moves, Poliwrath is weak to Electric and Grass type moves, and Crabominable is weak to Fire, Fighting, and Steel type moves.

• Bewear has the Fluffy ability, which halves the damage of moves that make contact, but doubles the damage it takes from Fighting type moves. Your best bet is to use special moves, Fire moves, or moves that don't make contact.
• Hariyama's Knock Off will do some serious damage if it uses it against a Pokémon with a held item, so beware.
• Crabominable has the Fightinium Z, so it can use its Z-Move, All-Out Pummeling.

Defeat Olivia. She uses Rock-type Pokémon. She has a level 54 Relicanth, level 54 Carbink, level 54 Alola form Golem, level 54 Probopass, and level 55 Midnight form Lycanroc. Rock types are weak to Water (Relicanth's part-Water typing negates this), Fighting (Carbink's part-Fairy typing negates this), Grass (Probopass' part-Steel typing negates this), and Ground. In addition, Relicanth is weak to Electric type moves, and Carbink is weak to Steel type moves.

• Both Golem and Probopass have the Sturdy ability, so you can't defeat them in one hit.
• Lycanroc has the Rockium Z, so it can use its Z-Move, Continental Crush.

Defeat Acerola. She uses Ghost-type Pokémon. She has a level 54 Sableye, level 54 Drifblim, level 54 Dhelmise, level 54 Froslass, and level 55 Palossand. Ghost types are weak to Ghost (Sableye's part-Dark typing negates this) and Dark (Sableye's part-Dark typing negates this as well). In addition, Sableye is weak to Fairy moves (its only weakness), Drifblim is weak to Electric, Rock, and Ice type moves, Dhelmise is weak to Fire, Flying, and Ice type moves, Froslass is weak to Fire, Rock, and Steel type moves, and Palossand is weak to Water, Grass, and Ice type moves.

• Try not to let Drifblim set up Amnesia, since it can use Baton Pass to pass the boosts to another Pokémon in her party.
• Sableye and Froslass have Confuse Ray, which can cause you problems if you're unlucky with your Pokémon hitting themselves in confusion.
• Palossand has the Ghostium Z, so it can use its Z-Move, Never-Ending Nightmare.

Defeat Kahili. She uses Flying-type Pokémon. She has a level 54 Skarmory, level 54 Crobat, level 54 Baile Style (Fire/Flying-type) Oricorio, level 54 Mandibuzz, and level 55 Toucannon. Flying types are weak to Rock (Skarmory's part-Steel typing negates this weakness), Ice (Skarmory's part-Steel typing and Oricorio's part-Fire typing negate this weakness), and Electric type moves. In addition, Skarmory is weak to Fire type moves, Crobat is weak to Psychic type moves, and Oricorio is weak to Water type moves.

• Skarmory has the Sturdy ability, so you can't defeat it in one hit. It also uses Spikes, so that your Pokémon take damage every time you switch them.
• Crobat and Oricorio can confuse your Pokémon, which can cause you problems if you're unlucky with your Pokémon hitting themselves in confusion.
• Don't use a move that makes contact while Toucannon's using Beak Blast; otherwise, it will cause your Pokémon to be burned.
• Toucannon has the Flyinium Z, so it can use its Z-Move, Supersonic Skystrike.

Defeat your fourth Elite Four member. A teleporter will then appear in the middle of the main Elite Four room. Go into it, then go up and sit in the chair. You'll get a cutscene with Professor Kukui, who tells you that you have to defeat him to become champion, then challenges you.

Defeat Professor Kukui. Unlike the Elite Four, he doesn't specialize in one type. He uses a level 57 Midday form Lycanroc, level 56 Alola form Ninetales, level 56 Braviary, level 56 Magnezone, level 56 Snorlax, and level 58 fully evolved form of the starter that the starter you picked is weak against.

• Lycanroc is Rock-type, so use a Water, Grass, Ground, or Fighting-type attack. Beware of Stealth Rock, which hurts your Pokémon when you switch them in (doing low damage to Pokémon that resist Rock type attacks, normal damage against Pokémon that have no weakness or resistance to Rock type attacks, double damage to Pokémon with a single weakness to Rock type attacks, and quadruple damage to dual type Pokémon whose types are both weak to Rock type attacks).
• Alola form Ninetales is Ice/Fairy-type, so use a Steel, Fire, Poison, or Rock type attack. Steel is especially good, since Ninetales takes quadruple the normal damage from it.
• Braviary is Normal/Flying-type, so use an Ice, Rock, or Electric type attack. Note that it has Tailwind, which doubles the speed of his entire team for 3 turns.
• Magnezone is Electric/Steel-type, so use a Fire, Fighting, or Ground type attack. Ground is especially good, since Magnezone takes quadruple the normal damage from it. It has the Sturdy ability, so you can't defeat it in one hit.
• Snorlax is Normal-type, so use a Fighting type attack.
• Incineroar is Fire/Dark-type, so use a Water, Ground, Fighting, or Rock type attack. It has the Firium Z, so it can use its Z-Move, Inferno Overdrive.
• Primarina is Water/Fairy-type, so use a Grass, Electric, or Poison type attack. It has the Waterium Z, so it can use its Z-Move, Hydro Vortex.
• Decidueye is Grass/Ghost-type, so use a Fire, Flying, Ice, Ghost, or Dark type move. It has the Grassium Z, so it can use its Z-Move, Bloom Doom.