To get the Silph Scope in FRLG, you must defeat Giovanni in the basement of the Rocket Game Corner in Celadon City.
You can access this area by pressing a hidden button behind the poster in the back of the Game Corner, which will open up the stairs to the basement.
Reaching Giovanni requires defeating many Rocket Grunts and solving simple puzzles. Once Giovanni is defeated, he will drop the Silph Scope, which you can then pick up.
Starting the Rocket Game Corner
In Celadon City, there is a big orange building called the Game Corner. This building has a lot of slot machines, as well as a poster in the back.
We need to get through the basement in order to get the Silph Scope, which will allow us to take on Pokémon Tower in Lavender Town.
Unlocking the Basement
In the back-right area of the Rocket Game Corner, by the counter, there is a poster on the wall with a Rocket Grunt standing in front of it.
We need to defeat this Grunt and interact with the poster to get to proceed through the Game Corner.
Simply interact with the Rocket Grunt to start the battle. There are no prerequisites for being able to fight him.
His Pokémon will be about level 20, though, so make sure your party is strong enough.
This is a pretty easy fight since the Grunt only has two fairly weak Pokémon:
After you beat this Grunt, just interact with the poster and the player will flip a switch, creating stairs in the corner.
Rocket Game Corner Basement
Once you’ve gone down the stairs, the goal is to get to the 4th basement floor.
This is where the Lift Key is, which is how we will reach Giovanni.
Getting to B3F is pretty straight forward, just take the stairs down. On B3F, though, there is a little maze to get through.
After clearing this first arrow puzzle, you will end on a yellow space. You can fight the Rocket Grunt staring you down, but it’s not necessary as long as you hug the wall.
If you choose to fight him, he has 3 Pokémon available:
- Rattata Lv 20
- Drowzee Lv 20
- Raticate Lv 20
After getting through the arrow maze, head down to the 4th basement floor and beat the Grunt in the northwest corner and he will drop the Lift Key.
He only has 2 Pokémon and is pretty easy to beat:
- Koffing Lv 21
- Zubat Lv 21
Don’t forget to pick up the Lift Key after you defeat this Grunt. Afterwards, you can head back upstairs to B2F.
Here, we need to head to the lift in the southeast corner.
This will require getting through another arrow puzzle maze.
After you’ve gotten through the maze, just continue to the right and you’ll come across the red lift doors.
Head inside, take the lift to the bottom basement floor (B4F), and defeat the two Grunts in front of the red gate.
You will need to defeat both Grunts, but you can heal between the battles. To start the battle just talk to one of them.
The left Grunt will have 3 Pokémon:
- Sandshrew Lv 23
- Sandslash Lv 23
- Ekans Lv 23
The right Grunt will also have 3 Pokémon:
- Ekans Lv 23
- Sandshrew Lv 23
- Arbok Lv 23
After beating these two Grunts, you can walk right up to Giovanni and challenge him to a fight. This battle will be a little tougher than the rest, so it may be a good idea to heal and save the game.
Giovanni also has 3 Pokémon in his party during the Rocket HQ fight:
- Onix Lv 25
- Rhyhorn Lv 25
- Kangaskhan Lv 29
As you can tell, these Pokémon are a lot stronger than the level 20 Zubats and Ekins that we’re used to, so make sure you’re prepared.
After defeating him, Giovanni will make an exit and leave a Pokéball on the ground.
This Pokéball will be the Silph Scope, which you can then pick up and use to clear the Pokémon Tower!