A light snow fills the brisk air of the quiet mountain town of Dendemille. Situated between Route 15 and Route 17, the town is home to both Madam Reminder and the Move Deleter. A cave known as Frost Cavern is located to the north.
Sycamore and his assistant Dexio appear as you enter the town. The professor imparts a few details about the legendary Pokémon, XerneasX / YveltalY. According to his research, those that saw it were so overwhelmed by its power, they were only able to describe it as resembling a certain letter. Dexio asks where a Pokémon like that could be, and the professor claims that when it loses all of its vitality, the legendary Pokémon goes to sleep in a secret place. As his research materials are 1,000 years old, not even he knows where it might be located.
Mr. Bonding can be found inside the local Pokémon Center. Speak to him to be awarded the Accuracy Power O-Power. Before leaving, talk to the woman near the Poké Mart to receive a Sitrus Berry.
Madam Reminder and Move Deleter
The southeast house belongs to Madam Reminder and the Move Deleter. In exchange for one Heart Scale, this old woman will help a Pokémon recall a move that it had forgotten. The old man's mind isn't what it used to be, but he can still help a Pokémon forget any move for free.
Mountain Pokédex rating
Continue up the street to the northeast house. The Monsieur inside would like to see how many Pokémon you've recorded in the Mountain Pokédex listing. If you have seen 70 or more, he will reward you with a Shell Bell.
The drifting snow and impenetrable fog make Frost Cavern a place full of fantastical illusions. Something is amiss in this frigid cavern, and only a thorough exploration into its icy depths will reveal the clues you need.
Cross the bridge to meet a Mamoswine and its Trainer. This Pokémon is usually happy to give rides through the deep snow on Route 17, but is upset over something in the Frost Cavern and won't budge from this spot. Follow the path northward to enter the cavern and investigate.
Head northeast to cross the first patch of ice. The path splits up ahead; turn east to fight Ace Trainer Neil and climb the stairs beyond.
Slide north over the ice to reach a hidden Ice Heal. Slide south, east, south, west, then north to the northeast edge. Go west and pass by Hiker Delmon. The path splits again; go northwest to Black Belt Alonzo, then slide south to Battle Girl Kinsey. From here, you can surf west to a stairway that leads to the floor below; this chamber houses both the Ice Rock and an Icy Rock. Work your way southeast over the ice from Kinsey; grab the Max Repel to the east, then surf south for a Never-Melt Ice before taking the southern stairs.
The Ace Trainer nearby will restore your Pokémon's health. A Hyper Potion lies to the south, atop a one-way shortcut to the entrance. Go north past Hiker Alain and climb the stairs.
Check the stalagmite for a hidden Super Potion and climb upstairs.
Work your way to the northwest for an Ether, then slide east to fight Black Belt Kenji. Stand opposite the stalagmite to the east; slide south, east, south, west, and south again to reach Battle Girl Gabrielle. Check the stalagmite for a hidden Elixir, and continue southeastward. Grab the Zinc from the second dead-end passage and go down the stairs.
Slide to the southeast corner. From here, slide northwest then south to reach TM79 (Frost Breath).
Backtrack to Black Belt Kenji and head north. A group of Team Flare members are harassing an Abomasnow, and its anger seems to be causing the blizzard outside. Take out the two Grunts with Trevor's help, then defeat Mable to rescue the agitated Pokémon.
The three troublemakers disappear, and Trevor leaves as well. Check on the Abomasnow to receive an Abomasite as a thank-you gift.
Route 17, or Mamoswine Road, is a treacherous route that connects Dendemille Town and Anistar City. Due to frequent snowstorms and heavy snowfall, it is impossible for humans to travel the area on foot.
Mamoswine was too worried about its friend Abomasnow before, but with the situation in Frost Cavern resolved, it is happy to help you navigate through the deep snow. Like the Rhyhorn on Route 9, this Pokémon can easily clear out any wayward boulders.
As you near the Anistar gate, you receive another Holo Clip. It's Serena/Calem, challenging you to a battle in front of the Anistar Gym.
Located between Route 17 and Route 18, Anistar City is famous throughout the region for its massive sundial, a mysterious device some believe originated in outer space. The seventh Gym is located here, and one of the residents is rumored to be knowledgeable about the lore of the legendary Pokémon.
Sycamore's assistant Sina is waiting for you just inside the city. She tells you that one of the residents knows about the legendary Pokémon, and gives you ten Repeat Balls to help you on your journey.
The girl outside the Pokémon Center is known as the Memory Girl. Her unique insight allows her to recount a Pokémon's memories. Show her any Pokémon you've obtained to learn its most important memories.
Stop by the Pokémon Center to find Mr. Bonding again. This time, he grants you the Exp. Point Power, which gives your Pokémon an experience boost after battle.
Also inside is a friendly Hex Maniac. Speaking to her will earn you up to four different TMs, but there's a catch—you can only get one per day, and it changes based on the time.
Visit the house next to the boutique and talk to the Psychic inside. He gives you TM10 (Hidden Power), a move that changes type depending on the Pokémon using it. Speak to him again to learn the type it will become when used by one of your Pokémon.
Learn the Story of the Legendary
Enter the house north of the boutique and speak to the Monsieur inside. This knowledgeable man recounts the story of the region's legendary Pokémon, XerneasX / YveltalY.
"It happened around 800 years ago. The Pokémon known as Xerneas used its shining horns to illuminate the lands of Kalos. At that very moment, people and Pokémon throughout the land felt great energy and vitality surge through their bodies. At the same time, a vast forest sprang up, with Xerneas at its center. Legend has it that, when it nears the end of its thousand-year life span, Xerneas releases all of its remaining energy, sharing it with all living things nearby. There's another story I know that talks of the appearance of just such a fortuitous Pokémon. Back 3,000 years ago, the Kalos region was engulfed in a terrible war. So the tale goes, a Pokémon came to the rescue of all the wounded Pokémon that had been caught up in the conflict. Some people suspect the Pokémon that appeared was Xerneas, but there's no way to know. Maybe they just wished a Legendary Pokémon had come to the rescue to brighten a tale of woe. Supposedly, after Xerneas had released its remaining energy, it transformed into a dried-up tree. It remains in hiding deep within the forest. According to old tales, as I say. Stories and tales."
"It happened around 800 years ago. The Pokémon known as Yveltal spread its ominous wings, engulfing the lands of Kalos in darkness. At that moment, people and Pokémon throughout the land began to fall one by one. Yveltal let out a piercing cry and took to the sky, vanishing to an unknown location. Stories say that when it nears the end of its thousand-year life span, Yveltal absorbs the life force of the living things around it in order to charge its own energy. Another tale talks of the appearance of just such a terrifying Pokémon. Back 3,000 years ago, the Kalos region was engulfed in a terrible war. According to the stories, a Pokémon appeared and stole the life force of countless living beings. Some people suspect the Pokémon that appeared was Yveltal, but there's no way to know. Maybe they're just using a Legendary Pokémon as a metaphor for war and pestilence. In the tales, after Yveltal finished storing the energy it had absorbed, it transformed into a kind of cocoon, remaining in hiding deep in the mountains. According to old tales, as I say. Tales and stories."
Lend a Pokémon
Visit the next house to the north to meet a lonely old man. Lend him a Pokémon of level 5 or less for some company to cheer him up. You can retrieve the Pokémon at any time.
Make your way to the Gym and Serena/Calem catches up to you, looking for another battle. Her/His team now consists of a level 44 Meowstic, a level 44 Absol, third-stage starter Pokémon at level 46, and a level 44 Jolteon, Flareon, or Vaporeon if you chose Chespin, Fennekin, or Froakie, respectively.
The Anistar Gym specializes in Psychic Pokémon. Use Bug, Ghost, Dark, and Fairy attacks to deal heavy damage, and avoid sending in Fighting or Poison Pokémon. Stand in the room's center to reveal the Gym's interior, a colorful, spherical maze that seems to float in outer space. Use the yellow warp panels to progress through the maze, from blue to green to pink paths, until you reach the Gym Leader on the bottom floor.
Defeated, Olympia awards you the Psychic Badge, which ensures obedience from all Pokémon up to level 90. She also gives you TM04 (Calm Mind) as a prize.
Outside, Serena/Calem returns for a rematch, but is interrupted by a Holo Clip from Lysandre. In a sickening revelation, you learn that he is Team Flare's leader, and he intends to use an "ultimate weapon" to eliminate everyone who isn't part of the group. Serena/Calem advises you to search for the team's headquarters; maybe Lysandre is where you first met him, in Lumiose City...