How to Get Flash in Pokémon Yellow: 9 Steps

What Is Flash in Pokémon Yellow?

Flash is HM05 in Pokémon Yellow. In battle, it lowers the opposing Pokémon’s accuracy. Outside battle, its main purpose is to illuminate dark caves, especially Rock Tunnel, the cave route between Route 10 and Lavender Town. Technically, brave players can stumble through Rock Tunnel without Flash, but that experience is less “classic adventure” and more “walking into furniture during a power outage.”

In Generation I games like Pokémon Red, Blue, and Yellow, HM moves are special because they can be used outside battle once the right conditions are met. They also cannot be removed from a Pokémon’s moveset through normal gameplay in Pokémon Yellow. That means you should think carefully before teaching Flash to a favorite team member, especially if you care about keeping strong battle moves.

Where Do You Get Flash in Pokémon Yellow?

You get Flash from one of Professor Oak’s aides in the gate building on Route 2. This building is located south of the Diglett’s Cave exit on the eastern side of Route 2. To receive HM05 Flash, you must have at least 10 Pokémon registered as caught in your Pokédex.

The keyword here is caught, not simply seen. Seeing a Pokémon in battle does not count toward the aide’s requirement. Your Pokédex needs to show 10 owned Pokémon. If you have only battled a Spearow, stared dramatically at a Jigglypuff, and watched a trainer’s Rattata ruin your day, none of that helps unless those Pokémon are actually registered as caught.

Before You Start: Requirements for Getting Flash

Before heading out to claim HM05 Flash, make sure you have the following:

• At least 10 caught Pokémon registered in the Pokédex.
• HM01 Cut, which you receive from the captain of the S.S. Anne.
• A Pokémon that knows Cut in your party.
• Access to Vermilion City and Diglett’s Cave.
• Enough healing items in case wild Diglett or Dugtrio cause trouble.

You will usually get Flash after visiting Vermilion City, clearing the S.S. Anne, and receiving Cut. This timing makes sense because the next major section of the game eventually sends you toward Rock Tunnel, where Flash becomes extremely helpful.

How to Get Flash in Pokémon Yellow: 9 Steps

Step 1: Progress Until You Reach Vermilion City

First, play through the story until you reach Vermilion City. By this point, you should have traveled through Pewter City, Mt. Moon, Cerulean City, and Route 24/25. Vermilion City is important because it gives you access to the S.S. Anne and Diglett’s Cave, both of which matter for getting Flash.

You do not receive Flash directly in Vermilion, but the city acts as the launchpad. Think of it as your “Flash preparation hub,” except with more sailors, electric Gym drama, and probably a Pikachu who refuses to enter its Poké Ball.

Step 2: Get HM01 Cut from the S.S. Anne

Board the S.S. Anne in Vermilion City and explore the ship. After battling your rival and helping the seasick captain, you receive HM01 Cut. Cut is required to remove small trees blocking certain paths, including areas around Route 2.

Teach Cut to a compatible Pokémon. In Pokémon Yellow, common Cut users include Pokémon such as Oddish, Bellsprout, Sandshrew, or similar early-game options depending on your version and trades. Since Pikachu cannot learn Cut, do not stare at it accusingly. It is already doing its best.

Step 3: Catch at Least 10 Different Pokémon

Professor Oak’s aide will only give you Flash if you have 10 Pokémon registered as owned in your Pokédex. If you are short, catch a few common Pokémon before making the trip.

Easy early-game Pokémon to help reach the 10-Pokémon requirement may include Pidgey, Rattata, Caterpie, Metapod, Weedle, Kakuna, Nidoran, Spearow, Jigglypuff, Abra, Magikarp, Diglett, and others depending on where you have explored. You do not need 10 Pokémon in your party or PC at that exact moment; the Pokédex ownership count is what matters.

A practical trick is to catch Pokémon while naturally traveling through early routes rather than waiting until the last second. Nobody wants to delay a major adventure because a Pidgey refused to stay inside a Poké Ball like it had an appointment elsewhere.

Step 4: Put a Pokémon That Knows Cut in Your Party

Before leaving Vermilion, check your party. You need a Pokémon that knows Cut because parts of Route 2’s eastern side are blocked by cuttable trees. If your Cut user is sitting in the PC, the game will not politely teleport it into your pocket. You must bring it with you.

Open your Pokémon menu and confirm that one of your party members has Cut. Also consider bringing a few Poké Balls if you still need more caught Pokémon, because Diglett’s Cave gives you another opportunity to add Diglett to your Pokédex.

Step 5: Enter Diglett’s Cave Near Vermilion City

From Vermilion City, head east to Route 11. Near the entrance to Route 11, you will find Diglett’s Cave. Enter it and prepare for a straightforward underground walk. As the name suggests, Diglett’s Cave mostly contains Diglett, with a small chance of encountering Dugtrio.

Be careful if you run into Dugtrio. It can be much stronger than the average wild Pokémon in the area, especially if your team is underleveled. If you are not ready to fight it, running away is a perfectly respectable strategy. This is not cowardice; this is resource management with dramatic footsteps.

Step 6: Travel Through Diglett’s Cave to Route 2

Continue through Diglett’s Cave until you emerge on the eastern side of Route 2. This side of Route 2 is separated from the early-game path by trees and ledges, which is why you could not fully explore it at the beginning of the game.

Once outside the cave, you are close to the aide who gives you Flash. The key is to head south from the Diglett’s Cave exit. You may pass a small house and a route area with trees. Use Cut where necessary to continue moving through the path.

Step 7: Find the Gate Building South of Diglett’s Cave

On Route 2, look for the gate building south of the Diglett’s Cave exit. This is not the same as a Pokémon Center or a regular house. It is one of the route connector buildings, and inside you will find one of Professor Oak’s aides waiting to check your Pokédex progress.

This part is where many players get turned around. If you accidentally wander back toward Pewter City or Viridian Forest, pause and reorient yourself. Your goal is the gate building on the eastern side of Route 2, south of the cave exit, not the main early-game path you used before Brock.

Step 8: Talk to Professor Oak’s Aide

Enter the building and speak with Professor Oak’s aide. He will check your Pokédex. If you have at least 10 Pokémon registered as caught, he gives you HM05 Flash.

If you do not meet the requirement, he will not give you the HM yet. In that case, leave, catch more Pokémon, and return. The requirement is simple but strict. Nine caught Pokémon is not “basically ten” in Professor Oak’s research economy.

Step 9: Teach Flash to a Compatible Pokémon

After receiving HM05, open your item menu, select HM05, and teach Flash to a Pokémon that can learn it. Many players prefer teaching Flash to a utility Pokémon rather than a main battler because Flash is not especially powerful in battle. Its accuracy-lowering effect can be useful in certain situations, but most teams have better combat options.

Once a Pokémon knows Flash, you can use it inside dark caves such as Rock Tunnel. Open the Pokémon menu while inside the cave, select the Pokémon that knows Flash, and use the move. The cave will light up, and suddenly Rock Tunnel becomes a real route instead of a blindfolded hiking simulator.

Best Pokémon to Teach Flash in Pokémon Yellow

Because HM moves cannot be forgotten normally in Pokémon Yellow, it is smart to teach Flash to a Pokémon you do not mind using as a support or utility member. Some players use a Pokémon that can carry multiple field moves, while others keep a dedicated “HM helper” in the party whenever exploration demands it.

Good candidates depend on your available Pokémon, but the general rule is simple: avoid teaching Flash to a key attacker if you would regret losing a move slot. In-game battles in Pokémon Yellow are not impossible with Flash on a main team member, but the move is much more valuable for navigation than raw battle strength.

Do You Actually Need Flash for Rock Tunnel?

Strictly speaking, you can complete Rock Tunnel without Flash. The layout still exists even when the screen is dark, and experienced players sometimes memorize the route or use maps. However, for most players, Flash makes the journey much easier and more enjoyable.

Without Flash, Rock Tunnel can feel slow, frustrating, and unnecessarily confusing. You may run into more wild Pokémon, miss ladders, loop through familiar areas, or start questioning whether the cave was designed by someone who personally disliked you. With Flash, you can see walls, paths, trainers, ladders, and the general shape of the tunnel.

Common Mistakes When Trying to Get Flash

Mistake 1: Having Seen 10 Pokémon Instead of Caught 10

The aide checks how many Pokémon are registered as owned. Seeing Pokémon does not count. If your Pokédex says you have seen plenty but caught fewer than 10, catch more Pokémon before returning.

Mistake 2: Forgetting to Bring Cut

Route 2’s eastern section requires Cut access. If your Cut user is in the PC, you may have to backtrack. Always check your party before entering Diglett’s Cave.

Mistake 3: Teaching Flash to the Wrong Pokémon

Since HM moves are permanent in normal Pokémon Yellow gameplay, do not rush. Pick a Pokémon that can spare the move slot.

Mistake 4: Looking in the Wrong Route 2 Building

The aide is in the gate building south of Diglett’s Cave on Route 2’s eastern side. If you are wandering near the Viridian Forest entrance, you are probably on the wrong side of the route.

Helpful Tips for Getting Flash Faster

If you want to get Flash quickly, build your Pokédex count as you progress naturally. Catch common Pokémon on Routes 1, 2, 3, 4, 24, and 25. Buy the Magikarp from the salesman near Mt. Moon if you want an extra owned Pokémon and do not mind paying for what is basically a floppy investment with future dragon-shaped potential.

You can also catch Diglett inside Diglett’s Cave before reaching the aide. This is convenient because you are already walking through the cave anyway. If you are lucky and encounter Dugtrio, you may register an even stronger Pokémon, though catching it can be more difficult.

Keep in mind that evolved Pokémon count separately in the Pokédex. For example, if you have caught Caterpie and evolved it into Metapod and Butterfree, those entries can help increase your owned count. Evolution is one of the easiest ways to increase Pokédex progress without hunting for entirely new wild encounters.

Why Flash Matters in Pokémon Yellow

Flash is one of those moves that players often underestimate until they need it. It does not deal damage, it is not flashy in battle despite literally being named Flash, and it takes up a valuable move slot. Still, for exploration, it plays a key role in smoothing out one of the most confusing mid-game areas.

Rock Tunnel is the main reason to get Flash. After you pass through Route 9 and reach Route 10, Rock Tunnel becomes the path toward Lavender Town. Lavender Town then opens the door to more of Kanto’s mid-game progression, including Pokémon Tower, Celadon City access, and later story events involving Team Rocket.

In other words, Flash is not just a random optional item sitting in a forgotten building. It is a practical tool that helps connect your early-game progress to the larger Kanto adventure.

Experience Notes: What It Feels Like Getting Flash in Pokémon Yellow

Getting Flash in Pokémon Yellow is one of those classic moments that quietly teaches players how old-school Pokémon exploration works. The game does not always point directly at your next objective. Instead, it drops clues, blocks paths with trees, places helpful NPCs in route gates, and expects you to remember that one cave near Vermilion City might connect to an area you saw hours ago.

The first time many players search for Flash, they assume it must be near Rock Tunnel. That would make sense, right? Dark cave, nearby light-up move, simple logic. But Pokémon Yellow has a charming habit of saying, “Good guess, now please walk halfway across Kanto.” By placing HM05 back on Route 2, the game encourages you to revisit earlier locations with new abilities. Cut is not just a tree-removal tool; it changes how the map feels.

The trip through Diglett’s Cave also creates a memorable little adventure. You enter from the Vermilion side expecting a basic tunnel, then suddenly wild Diglett pop up every few steps. Most are manageable, but then a Dugtrio appears and the mood changes instantly. It is like walking through a hallway full of garden snakes and suddenly meeting the landlord. If your team is not ready, Dugtrio can hit hard and move quickly, so this simple errand can briefly become a survival story.

The 10-Pokémon requirement is another smart design choice. It gently rewards players who explore and catch Pokémon instead of relying only on Pikachu and a couple of favorites. If you have been catching common Pokémon along the way, Professor Oak’s aide feels like a nice reward. If you have ignored the Pokédex completely, he becomes a polite roadblock in a lab coat.

One useful habit is to treat every early route as a chance to add at least one new Pokédex entry. Catch a Pidgey. Catch a Rattata. Grab a Caterpie or Weedle. Pick up a Nidoran if available. Buy Magikarp if you want to invest in future greatness while currently owning a fish that knows Splash. By the time you reach the Flash aide, the requirement will feel effortless.

The biggest personal lesson from this part of the game is to respect utility moves. Players often focus only on damage, levels, and type matchups, but Kanto rewards preparation. Cut opens paths. Flash lights caves. Later HMs like Surf and Strength expand the world even more. Flash may not win many battles, but it turns Rock Tunnel from a frustrating maze into a readable journey.

There is also a small strategic decision involved: who gets stuck with Flash? Since you cannot casually delete HM moves in Pokémon Yellow, teaching it to the wrong Pokémon can feel annoying later. Many experienced players prefer giving it to a support Pokémon rather than sacrificing a strong attacking move on a core team member. It is not the end of the world if you teach it to a regular teammate, but planning ahead keeps your movesets cleaner.

Overall, getting Flash is a perfect example of what makes Pokémon Yellow memorable. It combines exploration, backtracking, Pokédex progress, HM utility, and just enough confusion to make the solution satisfying. Once you finally receive HM05 and light up Rock Tunnel, it feels less like you found a move and more like you earned permission to stop walking into invisible cave walls.

Conclusion

To get Flash in Pokémon Yellow, catch at least 10 Pokémon, get Cut from the S.S. Anne, travel through Diglett’s Cave from the Vermilion side to Route 2, and talk to Professor Oak’s aide in the gate building south of the cave exit. Once you receive HM05, teach it to a compatible Pokémon and use it to brighten Rock Tunnel.

Flash may not be the most exciting move in battle, but it is one of the most useful exploration tools in the mid-game. It saves time, reduces frustration, and helps you move confidently toward Lavender Town. In a game where every route feels like a small puzzle box, HM05 is the light switch you will be very glad you found.

Note: Because HM moves cannot normally be removed in Pokémon Yellow, teach Flash to a Pokémon that can spare the move slot instead of rushing to place it on your strongest battler.