- Pokemon LeafGreen Flash is HM05, the field move that lights up dark caves such as Rock Tunnel.
- Register 10 caught Pokemon in your Pokedex, then visit Professor Oak's aide on Route 2.
- The Cascade Badge from Misty is required to activate Flash outside of battle.
- Teach it before leaving Cerulean City for Route 9, Route 10, and Rock Tunnel.
- Pikachu, Clefairy, Abra, and Jigglypuff are dependable early Flash users.
What Is Pokemon LeafGreen Flash (HM05)?
Pokemon LeafGreen Flash is the player shorthand for HM05, one of the seven Hidden Machines scattered across Kanto. Taught to a Pokemon like a regular TM, Flash does two things: outside battle it illuminates pitch-black caves, and inside battle it works as a Normal-type move that lowers the opposing Pokemon's accuracy by one stage. In practice, the overworld effect is the only reason to carry it.
The single most important destination for Flash is Rock Tunnel, the dark cave linking Route 10 to Lavender Town on the road between Cerulean City and the next story beats. Without Flash, the tunnel stays almost completely black, turning a straightforward cave walk into a slow crawl of blind wild encounters and missed turns.
| Attribute | Details |
|---|---|
| Item | HM05 Flash |
| Pickup location | Route 2 gate building, Professor Oak's aide |
| Unlock requirement | At least 10 caught Pokemon in the Pokedex |
| Badge requirement | Cascade Badge (Misty, Cerulean City Gym) |
| Field effect | Lights up dark caves such as Rock Tunnel |
| Battle effect | Normal-type move, lowers target accuracy one stage |
| Move removal | Move Deleter in Fuchsia City only |
Because Flash is an HM, a Pokemon that learns it cannot overwrite the move through level-up or TMs. Only the Move Deleter in Fuchsia City can remove it, so think about which team member you dedicate to utility duty before teaching it.
This guide applies to both the 2004 Game Boy Advance original and the current Nintendo Switch re-release, which keeps the same Kanto layout, item locations, and HM system. You can verify the current version on the official Nintendo store page.
How to Get HM05 Flash: Step-by-Step
The Flash pickup is easy to miss because Oak's aide will not hand it over until your Pokedex shows real catching progress. Follow this sequence and you will have the move long before Rock Tunnel becomes relevant.
Catch 10 Pokemon
Register ten species as caught, not just seen. Early routes make this fast: Pidgey and Rattata fill slots on Route 1 alone, and Viridian Forest adds Bug and Flying types within minutes.
Earn the Cascade Badge
Defeat Misty at the Cerulean City Gym. The Cascade Badge is what authorizes Flash use in the field, so the move stays dormant in your bag without it.
Travel to the Route 2 Gate
Head to the gate building on Route 2 between Pewter City and Viridian Forest. This is where Professor Oak's aide waits inside the passage building.
Talk to Oak's Aide
Speak with the aide and let him check your Pokedex. With ten or more caught Pokemon registered, he hands over HM05 Flash on the spot.
Teach Flash to a Pokemon
Open the bag, select HM05, and teach it to a compatible team member. Pikachu, Clefairy, Abra, and Jigglypuff all qualify and are catchable before this point.
| Easy Catch | Location | Why It Helps |
|---|---|---|
| Pidgey | Route 1 | Extremely common, caught with one or two Poke Balls |
| Rattata | Route 1 | Fills a Pokedex slot in minutes |
| Spearow | Route 3 | Fast encounter rate east of Pewter |
| Nidoran (both) | Route 22 and Route 3 | Two families count separately |
| Pikachu | Viridian Forest | Counts toward the total and learns Flash itself |
| Bellsprout | Routes 5-8 and 12-15 | LeafGreen version encounter, easy catch |
The aide checks caught entries only. Walking past wild Pokemon does nothing for the requirement, so actually throw Poke Balls. Weakening a target to low red HP and applying sleep or paralysis makes ten catches a quick chore rather than a grind.
Where to Use Flash: The Rock Tunnel Route
Rock Tunnel sits east of Cerulean City and is the only mandatory dark cave in the main story. The standard approach runs through Route 9 and Route 10, and Flash turns the tunnel from a blind maze into a readable map with visible ladders, trainers, and item balls.
| Route Step | Location | What to Do |
|---|---|---|
| 1 | Route 9 | Leave Cerulean eastward, clear the trainer line |
| 2 | Route 10 north | Heal at the Pokemon Center near the tunnel mouth |
| 3 | Rock Tunnel entrance | Activate Flash before stepping inside |
| 4 | Rock Tunnel interior | Follow the lit path, fight trainers, grab items |
| 5 | Route 10 south | Exit toward Lavender Town and the next story arc |
Rock Tunnel packs wild Pokemon in their mid teens plus several trainers, and Lavender Town is still a full cave away. Heal before entering and carry Repels, Potions, and an Escape Rope so a bad run never costs you real progress.
One bonus for later: Route 10 also borders the Power Plant, where Zapdos waits. That area needs Surf, which arrives much later in the story, so note the location and return after the Fuchsia City leg of the adventure. The full regional layout is documented on the official Pokemon game page.
Best Pokemon to Teach Flash Before Rock Tunnel
Any of the four Pokemon below can carry Flash without hurting your battle plan, and every one of them is obtainable before the Cerulean City stretch ends. Pick based on what else the slot contributes.
Pikachu
- Caught in Viridian Forest before the first badge
- Doubles as your answer to Misty
- Fast, reliable, and on the main route anyway
Clefairy
- Caught in Mt. Moon during normal progression
- Bulky enough to absorb Rock Tunnel hits
- Flexible support movepool later
Abra
- Caught on Routes 24 and 25
- Teleport gives free dungeon exits
- Grows into a top-tier Psychic attacker
Jigglypuff
- Caught on Route 3 east of Pewter
- Sing makes future catching easier
- High HP cushions blind encounters
| Flash User | Catch Location | Best Extra Utility |
|---|---|---|
| Pikachu | Viridian Forest | Electric damage vs Misty and Flying types |
| Clefairy | Mt. Moon | Defensive bulk and status support |
| Abra | Routes 24-25 | Teleport escapes, future Psychic power |
| Jigglypuff | Route 3 | Sing for catching, high HP buffer |
Many players dedicate one slot to a utility Pokemon that carries Flash and Cut while the core four or five members keep clean, powerful movesets. This keeps your main attackers from wasting slots on field moves they will never use in battle.
Flash Compared to the Other LeafGreen HMs
Flash is one of only two HMs you can secure before the third badge, which makes it a foundational exploration tool rather than a late-game luxury. Here is how it fits into the full Hidden Machine set.
| HM | Move | Location | Field Use |
|---|---|---|---|
| HM01 | Cut | S.S. Anne, Vermilion City | Removes small blocking trees |
| HM02 | Fly | Route 16 hidden house | Fast travel between visited towns |
| HM03 | Surf | Safari Zone Secret House | Travel across water |
| HM04 | Strength | Fuchsia City, return Gold Teeth | Pushes boulders in caves |
| HM05 | Flash | Route 2 gate building | Illuminates dark caves |
| HM06 | Rock Smash | Ember Spa, One Island | Breaks cracked rocks |
| HM07 | Waterfall | Icefall Cave, Four Island | Climbs waterfalls |
Before Entering Rock Tunnel:
- Caught 10 Pokemon and received HM05 Flash from Oak's aide
- Earned the Cascade Badge from Misty in Cerulean City
- Taught Flash to Pikachu, Clefairy, Abra, or Jigglypuff
- Stocked Potions, Repels, and an Escape Rope
- Healed at the Route 10 Pokemon Center
With Flash active, Rock Tunnel becomes a routine cave, Lavender Town opens up, and the story pushes cleanly toward Celadon City, the Pokemon Tower, and the Team Rocket Hideout. Handle it early and the mid-game flows without friction.
Pokemon LeafGreen Flash FAQ
Q: Is Flash required to enter Rock Tunnel in Pokemon LeafGreen?
No. The game allows you to walk into Rock Tunnel without Flash, but the screen stays almost entirely dark, so navigation becomes trial and error. Most players treat Flash as a practical requirement because the lit cave is dramatically easier to map and clear.
Q: Can I get Flash before beating Brock?
Yes. The only pickup requirement is 10 caught Pokemon in the Pokedex, and Oak's aide stands in the Route 2 gate near Pewter City. However, you need the Cascade Badge from Misty before Flash can actually be used outside of battle.
Q: How do I remove Flash from a Pokemon?
Visit the Move Deleter in Fuchsia City. HM moves like Flash cannot be overwritten by level-up moves or TMs in LeafGreen, so the Move Deleter is the only way to free the slot.
Q: Which Pokemon is the best Flash user?
Pikachu is the most convenient choice because Viridian Forest places it on your route before the first badge, and it also helps against Misty. Clefairy, Abra, and Jigglypuff are solid alternatives if your team already covers Electric damage.