After meeting Wulfric in the Pokémon Village and exploring the area, you should challenge the Snowbelle Gym.
Gym Information
Wulfric's gym features Ice-type pokémon. Ice-type pokémon are weak to Fire, Fighting, Rock, and Steel moves.
Battle Trainers
The first trainer you can challenge is Ace Trainer Imelda, who stands on the pink platform on the left.
Ace Trainer Imelda
Ace Trainer Imelda has a level 54 Sneasel (very weak to Fighting, weak to Rock, Bug, Steel, Fire, and Fairy) and a level 55 Cloyster (weak to Fighting, Rock, Grass, Electric).
The Sneasel's moves are Slash (Normal physical attack), Snatch (causes the next status-affecting move to affect Sneasel instead of the target), Punishment (Dark physical attack), and Ice Shard (Ice physical attack).
The Cloyster's moves are Aurora Beam (Ice special attack), Spike Cannon (Normal physical attack), Spikes (causes damage on switching out) and Icicle Crash (Ice physical attack).
Rotate the Gym
After the battle with Imelda, step on the pink switch TWICE to rotate the pink cubes that are south of you. After that, you should be able to go south, then walk east on the pink cubes, then go north onto the blue platform with the next trainer.
Ace Trainer Viktor
Ace Trainer Viktor has a level 54 Delibird (very weak to Rock, weak to Steel, Fire, Electric) and a level 55 Mamoswine (weak to Fighting, Steel, Fire, Water, Grass).
The Delibird knows Present, which can randomly damage or heal you.
The Mamoswine's moves are Blizzard (Ice special attack), Earthquake (Ground physical attack), Thrash (Normal physical attack), and Mist (prevents stat changes).
Rotate the Gym Again
After you have defeated both Imelda and Viktor, step on the blue switch three times, then go south and step on the pink switch three times. Now you should be able to use the middle bridges to go north onto the yellow cubes. From there, you can walk onto the green platform on the right.
Ace Trainer Shannon
Ace Trainer Shannon has a level 52 Cryogonal (weak to Fighting, Rock, Steel, Fire), a level 53 Piloswine (weak to Fighting, Steel, Fire, Water, Grass), and a level 54 Jynx (weak to Rock, Bug, Ghost, Steel, Fire, Dark).
The Cryogonal's moves are Reflect (prevents damage for one turn), Slash (Normal physical attack), Confuse Ray (causes confusion) and Recover (heals up to 50% of HP).
The Piloswine's moves are Mist (prevents stat changes), Thrash (Normal physical attack), Earthquake (Ground physical attack) and Blizzard (Ice special attack).
The Jynx's moves are Wake-Up Slap (Fighting physical attack), Avalanche (Ice physical attack), Body Slam (Normal physical attack) and Wring Out (Normal special attack).
Rotate the Gym Once More
After the battle, go north onto the green cubes, then west, then south onto the yellow platform.
Ace Trainer Theo
Ace Trainer Theo has a level 54 Beartic (weak to Fighting, Rock, Steel, Fire) and a level 55 Vanilluxe (weak to Fighting Rock, Steel, Fire).
The Beartic's moves are Icicle Crash (Ice physical attack), Rest (causes user to fall asleep and recover all HP, then wake up after three turns), Blizzard (Ice special attack) and Hail (causes the Hail weather condition, which damages all non-Ice pokémon each turn).
The Vanilluxe's moves are Acid Armor (sharply increases the user's Defense), Ice Beam (Ice special attack), Hail (causes the Hail weather condition, which damages all non-Ice pokémon each turn), and Mirror Coat (Psychic special attack).
Rotate the Gym a Final Time
Step on the yellow switch, then step on the green switch three times. Then go south, then use the middle bridge to go north. You can walk up the stairs to the north to reach Gym Leader Wulfric.