You’ll get HM05 Flash from one of Prof. Oak’s aides in a building on Route 2. Though he’ll only give you the HM if you’ve caught at least 10 different Pokémon (including evolutionary forms).
You’ll also need to use HM01 Cut to chop down a tree blocking your path into the building where the aide is located.
So you can get HM05 at any point after you get HM01.
Prerequisites
This is what you need to do before you can get HM05:
- Obtain HM01 Cut from the ship captain on the S.S. Anne in Vermillion City
- Obtain the Cascadebadge by defeating Misty in Cerulean City
- Have a Pokémon in your party that knows Cut
Getting HM05 Flash
Starting from the Vermillion City Pokémon Center, head southeast.
When you reach the officer next to the Poké Mart, head east towards Route 11.
Once you reach the entrance of Diglett’s Cave, go inside.
Go down the ladder into the main section of the cave.
Walk northwest along the path until you reach the end.
Go up the ladder at the end of the path.
Head outside the cave and onto Route 2.
After exiting the cave, head southeast following the path.
You’ll eventually reach a tree below a house blocking your path. Use Cut to chop it down.
Keep heading south and enter the large building.
Inside the building, you’ll find Prof. Oak’s aide.
If you talk to him, he says he’ll give you HM05 if you’ve caught at least 10 different kinds of Pokémon.
If you’re unsure of how many Pokémon you’ve caught, check your Pokédex.
Note: Evolving a Pokémon also adds to the number of Pokémon you’ve caught. For example, if you have a Charmander and it evolves into Charmeleon, Charmeleon will count as another Pokémon you’ve caught.
Because of this, Catching Caterpie is a useful way to fill a few spaces in your Pokédex. It evolves into Metapod at Level 7, and then into Butterfree at Level 10.
Note: To use Flash outside of battle, you first need to obtain the Boulderbadge by defeating Brock in Pewter City.
Flash Move Details
| Flash Move Details | |
|---|---|
| Type | Normal |
| Power | 0 |
| Accuracy | 70% |
| PP | 20 (max. 32) |
| Effect | Lowers opposing Pokémon’s accuracy by one stage. Outside of battle, lights up dark areas. |
As a move in battle, Flash has limited use.
With 0 power, Flash won’t damage an opponent’s Pokémon.
And while lowering an opponent’s accuracy can prove to be useful, there’s other battle strategies that prove to be more effective.
Being an HM also means that Flash can be taught an unlimited amount of times to multiple different Pokémon.
Outside of battle, Flash lights up dark areas such as caves and makes your surroundings visible.
However, Flash isn’t required to beat the game. Despite being much more difficult, it is technically possible to traverse through dark areas (like Rock Tunnel) without lighting them up.
Fun Fact: Pikachu Can Light Up Dark Areas
If Pikachu learns Thunderbolt or Thunder (either by leveling up or TM) while in the Rock Tunnel, talking to it will temporarily light up any dark area you’re currently in.
This will only work until you leave the Rock Tunnel or walk outside the area where Pikachu learns Thunderbolt or Thunder.
Also, unlike when using Flash, the Rock Tunnel will not stay illuminated while you walk around with the Pikachu this way. The cave will become dark again after Pikachu’s animation finishes.
So while this is a fun obscure secret exclusive to Pokémon Yellow, it is not recommended as a substitute for Flash.
Guide Navigation
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Pokémon Yellow
- How To Get HM05 Flash in Pokémon Yellow
