During your post-game quest, meet Cheren at Route 5 then he will go to Victory Road. Meet him at the cave that is the exit to the Pokémon League so you can battle him. You can battle him once per day. For this round, he adds Gigalith and Haxorus. Gigalith holds Leftovers so it slightly regains HP every turn and will use Stealth Rock to injure those who switch out. Haxorus holds a Dragon Gem, making its Outrage even more powerful for one use until becoming confused after 2-3 turns. The starter Pokémon holds a Focus Sash, allowing it to survive any attack if full on HP for one use. You’ll need a whole variety of moves for this battle. ... https://www.youtube.com/watch?v=RAR_SR63p_A
During your post-game quest, explore the Relic Castle and go through the deeper parts of the ruins. Navigate some rooms and find the room with Volcarona in it. Save your game before you interact. Volcarona is on Level 70. Don’t make contact with it or else you’ll get burned due to its Flame Body ability. Because it’s Bug/Fire type, Net Balls work best. If it reaches Level 100, it will learn its signature move, Fiery Dance. The move has a 50% chance of raising the user’s Special Attack stat.
...
https://www.youtube.com/watch?v=fzpMl-m1h2k
A Lakitu will appear and throw a spiked crawler onto the turf known as a Spiny. After collecting some coins and seeing some flashing blocks, you can go down the pipe for more coins or continue towards some flashing blocks. Cross the big stairway and hit a block containing multiple coins before going to the flagpole.
...
https://www.youtube.com/watch?v=aNJ2KHZ7Ckw
At the start, you’ll see a Martian and 2 platforms moving sideways. There are red kittens on some of the mushroom towers. Collect some coins and you’ll see 2 platforms connected to a line. Stand on one side and the platforms will adjust but will both fall if you stand on one side too long. Continue ahead and cross one more 2-platform set to reach the flagpole.
...
https://www.youtube.com/watch?v=X7ZXSma4vkw
Lt. Surge is one of the Kanto Leaders in the Pokémon World Tournament that can be battled in either the Kanto Leaders or World Leaders Tournaments. Lt. Surge is skilled in using Electric type Pokémon. Raichu will use Thunderbolt with an Electric Gem taking effect for once to power it up. Electrode will use Magnet Rise to avoid Ground type moves for 5 turns and Mirror Coat to draw back special attacks for double the damage. Magnezone holds an Air Balloon and will use Barrier to increase its Defense stat. Electivire will use Rock Tomb to slow opponents down and Low Kick on heavier foes. Jolteon will use Rain Dance to make Thunder unavoidable. Ampharos will use Charge and Cotton Guard to make itself much more defenseful. A move like Earthquake will easily damage the opponents.
...
https://www.youtube.com/watch?v=U_UnZiBN0h0
The beginning has a Piranha Plant with a spiked ball over it. Kick a Koopa shell to knock out the enemies ahead. Up ahead are some white blocks and Buster Beetles throwing some. Hit the P Switch to invert the garbage blocks in the sky to coins. Continue ahead and you’ll find the goal.
...
https://www.youtube.com/watch?v=KApWM6epwpg
In the Semitt Falls Cavern, there is a treasure chest containing the Exit spell, which enables you to immediately exit dungeons while on the map. Suddenly, after opening the chest, a Land Turtle will appear. This turtle is somewhat defenseful, and your physical attacks won’t do as much damage. However, it is weak against ice spells, so if you know any, be sure to use them. After defeating the turtle, explore more of the cave.
...
https://www.youtube.com/watch?v=RzkihCGjp-Q
Violet City’s gym leader, Falkner uses Flying type Pokémon. Rock types have an advantage over Flying types but be careful as the opponents counterfeit using Mud-Slap. Pidgeotto will use Gust for basic damage if you’re armed with either Bug or Grass types. After winning, you’ll receive the Zephyr Badge and a TM31 (Mud-Slap). Mud-Slap is a weak Ground type attack that lowers the target’s Accuracy stat.
...
https://www.youtube.com/watch?v=9s6TsCxWSLU
After getting all 8 gym badges, go west from Viridian City to Route 22 to encounter your rival once again. For the 7th battle, he adds Rhyhorn to his team. Alakazam has a nasty attack called Psychic that can sometimes lower the Special stats of the target. After the battle, continue west to the Pokémon League.
...
https://www.youtube.com/watch?v=ucLTI1Y57jk
At the beginning, you’ll see a Chain Chomp. Fly at the beginning to reach a pipe. In the secret room, you can get a Music Box to finish or go up the pipe to enter a secret pit below the course. Hit the P Switch to reveal white coins that form the number 3. The rest of the level has chomping plants. Some move slowly and they will jump if you leap over them. Continue ahead and you’ll find the goal.
...
https://www.youtube.com/watch?v=iiMwRxfq624