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Author Topic: Pokémon Yellow - easy walk through walls glitch  (Read 8728 times)

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Evie the Bird Mother ❤✿

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Pokémon Yellow - easy walk through walls glitch
« on: June 03, 2013, 12:14:36 pm »
This is an easier version of the walk through walls glitch that doesn't require a poisoned Pokémon or Super Glitch. I've only got it to work in Yellow, though. Basically, you just have to do the steps of Paco81's Hooked Dragonite glitch (to get this to work you can get your remaining steps to about 40 or so while you're in the Safari Zone) but talk to the NPC from the right when he's one tile down from the Pokémon Center door instead of from the left.

This will cause you to move automatically and the Start menu to keep popping up. The down button will be disabled, but only until you Fly away. If you hold B after closing the menu you can walk through walls anywhere you want. For some reason, different NPC sprites can appear in the wrong places and the S.S. Anne NPC in Vermilion City gets removed entirely.

To remove the walk through walls effect and bring the NPC back to his original spot, you can just enter a door.

Video: Here
« Last Edit: June 03, 2013, 12:15:50 pm by Torchickens »

(Image © Sanrio, Nintendo, HAL Laboratory)

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Re: Pokémon Yellow - easy walk through walls glitch
« Reply #1 on: June 05, 2013, 10:16:49 am »
Cool, good to know that this glitch is possible without struggling to get a poisoned Pokemon. However, holding B all the time is a little bit tiring.
Also, it's very good to know that effects of the Hooked Dragonite glitch happen to differ depending on the player's position while talking to the NPC. This really makes me wonder if there are more amazing effects to discover.

And this museum guy's "YOU HAVE TO GO" look is pure win.
qÁF qÁF qÁF qÁF qÁF qÁF qÁF qÁF qÁF qÁF qÁF qÁF qÁF qÁF qÁF qÁF qÁF qÁF qÁF qÁF qÁF qÁF qÁF qÁF qÁF qÁF

camper

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Re: Pokémon Yellow - easy walk through walls glitch
« Reply #2 on: June 05, 2013, 10:23:49 pm »
Can you encounter Pokemon while following someone? One of the positions I tried brought me down to the Route 2 grass patch, then out of bounds. I wonder if entering a battle ends this effect.
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Evie the Bird Mother ❤✿

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Re: Pokémon Yellow - easy walk through walls glitch
« Reply #3 on: June 06, 2013, 07:46:04 am »
Can you encounter Pokemon while following someone? One of the positions I tried brought me down to the Route 2 grass patch, then out of bounds. I wonder if entering a battle ends this effect.

I'm unable to get a battle when the follow-me effect is active, but I don't know for sure. If you force an encounter with 01xx58D0, the game will freeze for a moment before the battle. If in the impossible case this happens in the NPC's normal path before the glitch/in Pewter City after the glitch, you won't be able to press A or B to continue the battle like in the Hooked Dragonite glitch.

If this happens after moving to another location, you will be able to use A/B but not down (unless you Fly away). Ending the battle disables the automatic start button effect/re-enables down/makes you stop walking automatically, like if you encounter a Trainer or enter a door. This causes the "It's right here!" message to appear the next time you go to Pewter City.

(Image © Sanrio, Nintendo, HAL Laboratory)

I want to be a mother. 🦋 ✿

✿ Hi, I'm Evie. Sex male, and spiritually doesn't believe 'male'/'female' needs to be defined; lives more stereotypically like a woman. Call me whichever pronouns you like. :)

Please note:

While I'm one of the staff who runs the site, Abwayax is the founder and manages the technical side of the site (specifically the server, but I can do forum/wiki stuff if you like, I suggest if you do to make a thread about it to gather a consensus). Still feel free to contact me about higher site issues though; I will forward them to Abwayax if needed. :)

Forgiveness.

I feel that the more people pray to our greatest source/God/mathematical equality for world peace, the more and more it manifests into reality (until our next spiritual death).

Thank you Nyapon for this lovely artwork. :3

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Re: Pokémon Yellow - easy walk through walls glitch
« Reply #4 on: June 06, 2013, 09:43:24 am »
What causes the player to walk through walls? I've tried many positions in Red but so far I can only get the Start menu to pop up. Is the WTW effect exclusive to Yellow?
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Evie the Bird Mother ❤✿

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Re: Pokémon Yellow - easy walk through walls glitch
« Reply #5 on: June 06, 2013, 10:33:00 am »
What causes the player to walk through walls? I've tried many positions in Red but so far I can only get the Start menu to pop up. Is the WTW effect exclusive to Yellow?

I'm not sure. I believe the WTW effect is exclusive to Yellow, yes.

(Image © Sanrio, Nintendo, HAL Laboratory)

I want to be a mother. 🦋 ✿

✿ Hi, I'm Evie. Sex male, and spiritually doesn't believe 'male'/'female' needs to be defined; lives more stereotypically like a woman. Call me whichever pronouns you like. :)

Please note:

While I'm one of the staff who runs the site, Abwayax is the founder and manages the technical side of the site (specifically the server, but I can do forum/wiki stuff if you like, I suggest if you do to make a thread about it to gather a consensus). Still feel free to contact me about higher site issues though; I will forward them to Abwayax if needed. :)

Forgiveness.

I feel that the more people pray to our greatest source/God/mathematical equality for world peace, the more and more it manifests into reality (until our next spiritual death).

Thank you Nyapon for this lovely artwork. :3

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Re: Pokémon Yellow - easy walk through walls glitch
« Reply #6 on: April 05, 2015, 02:24:52 am »
I've made a bit of research, and it appears that memory address $CD38 allows to walk through walls.
It makes sense, because the developers may have thought that their paths wouldn't need any collision detection, because they are correctly programmed, so they removed the hitboxes while following someone to spare CPU time (extrapolation here !).

But why does the glitch pull up ?
It appears that, as soon as you begin following a path, RAM address CD38 is decreased every step. Once it equals zero, the game does something... with both Pewter guys, it makes their last dialogue pop up. I don't know what handles this.
Path data seems to be written from CCD2 onwards, and in the case of our bug the path is too long ; it overwrites CD38 and there you go !
(I tested editing the values CCD3~CD37 before moving, and it effectively changed my path)

(After tests) According to a comment in Pokered disassembly, path data is written before CCD3 (I doubt it though)
To explain how the code works, I need to understand how the FillMemory routine works. Sadly, this code's location isn't referenced anywhere, and it was a struggle to find it. FillMemory is at 0:36E0. So what does it do ? Does it go for- or backwards ? (How does the ldi instruction work ?)

According to VBA Disassembler :
Code: [Select]
FillMemory::
36E0: push de
36E1: ld d, a
36E2: ld a, d
36E3: ldi (hl), a
36E4: dec bc
36E5: la a, b
36E6: or c
36E7: jr nz, 36E2h
36E9: pop de
36EA: ret

[Time passed on https://github.com/iimarckus/pokered/: 2 hours]
Okay, found this in wram.asm
Quote from: IIMarckUs
wSimulatedJoypadStatesIndex:: ; cd38
; the next simulated joypad state is at wSimulatedJoypadStatesEnd plus this value minus 1
; 0 if the joypad state is not being simulated
   ds 1

wOverrideSimulatedJoypadStatesMask:: ; cd3b
; mask indicating which real button presses can override simulated ones
; XXX is it ever not 0?
   ds 1

   ds 1
By putting CD3B to hex:00, the player can't move and the B button doesn't work until the START menu pops up again. This seems to be another important part on how the glitch works.

Also, I've done a bit of testing, and there I can say : CD38, for an unknown reason, does only decrease each time the start menu is closed. No idea why. But this would explain why it continuously pops up :
  • The path data is written, and overflows to CD38.
  • The game reads unrelated data a path data (in my case, CD78 due to CD38 holding FA)
  • The game simulates joypad actions, and because many of these have a particular bit set, they are considered as Start button pressures
  • As long as the game doesn't simulate a pressure, CD38 remains unchanged. And when the player "overrides" the simulation (thanks to CD3B being hex:FA), the game doesn't decrement CD38, so upon releasing the Start menu pops up and CD38 gets decremented


Can you encounter Pokemon while following someone? One of the positions I tried brought me down to the Route 2 grass patch, then out of bounds. I wonder if entering a battle ends this effect.
I don't know, but I can tell that warps are active while following the Youngster. Also, path data is written onto memory used within battle, so if you could encounter wild Pokémon while following the Youngster, you may screw the path. I haven't seen any protections against wild encounters in the disassembly, though.


What causes the player to walk through walls? I've tried many positions in Red but so far I can only get the Start menu to pop up. Is the WTW effect exclusive to Yellow?

I'm not sure. I believe the WTW effect is exclusive to Yellow, yes.
I tested on English Blue, and it worked, so WTW isn't exclusive to Yellow.

I've tried a bit more places to talk him from, and the images are the result :
  • Talk to him from the first spot for a different walk through walls with less Start menu popup, but also functional. To go up/down, you MUST hold also left/right. Don't know why. Untested in Yellow.
  • I also found that if you talk to him from the spot shown on the second image, after closing the Start menu enough times, he leads you near the edge of the map, stuck in a rock. Going left leads you to a freeze tile ;D.
  • He also can actually lead you out of bounds if you talk to him from the third spot, answer no, then close the menu 13 times.
  • Talking to him next to the sign makes you enter the Museum ; upon exiting, he will go down... and disappear. OMG AN UFO KIDNAPPED HIM !!!
  • Standing on the fourth spot then talking to him will make you travel a few steps, then the game lockups.
  • Standing instead one tile north, he will lead you to a freeze tile.
  • Standing one more tile north and stopping him will also trap you like the second spot ; but he will, during one second, appear as a glitchy mess right north of you.
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Re: Pokémon Yellow - easy walk through walls glitch
« Reply #7 on: April 05, 2015, 12:20:14 pm »
To explain how the code works, I need to understand how the FillMemory routine works. Sadly, this code's location isn't referenced anywhere, and it was a struggle to find it. FillMemory is at 0:36E0. So what does it do ? Does it go for- or backwards ? (How does the ldi instruction work ?)
ldi (hl), a (written as ld [hli], a in RGBDS syntax) is equivalent to ld (hl), a plus inc hl. The effect of the function is, as noted in pokered’s home.asm, “Fill bc bytes at hl with a.”

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Re: Pokémon Yellow - easy walk through walls glitch
« Reply #8 on: June 10, 2015, 03:17:43 am »
I recently bought a Pokémon Rouge (French Red) cartridge, and in this version, this glitch doesn't work along with the Amazing Man glitch (I think there is a link between these). As soon as I enter Pewter City, I get the museum dialog, then the guy teleports away. But as soon as I move, he pops back straight next to the Mart.

I'm going to try entering Pewter City not through the Mart (either re-entering the Safari Zone, then Digging out 1. to Pewter City Pokémon Center or 2. to another Pokémon Center, then entering Pewter city by a) Walking (probably from Viridian City) or b) Flying ; or blacking out)

Can this glitch be performed in European R/B versions using the Walk around with only fainted Pokémon glitch ? I doubt it, but maybe...

Just an aparté : the Amazing Man glitch doesn't teleport NPCs, but their orientation remains South-facing until the START menu is closed.
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Re: Pokémon Yellow - easy walk through walls glitch
« Reply #9 on: June 11, 2015, 10:52:26 am »
I recently bought a Pokémon Rouge (French Red) cartridge, and in this version, this glitch doesn't work along with the Amazing Man glitch (I think there is a link between these). As soon as I enter Pewter City, I get the museum dialog, then the guy teleports away. But as soon as I move, he pops back straight next to the Mart.

I'm going to try entering Pewter City not through the Mart (either re-entering the Safari Zone, then Digging out 1. to Pewter City Pokémon Center or 2. to another Pokémon Center, then entering Pewter city by a) Walking (probably from Viridian City) or b) Flying ; or blacking out)

Can this glitch be performed in European R/B versions using the Walk around with only fainted Pokémon glitch ? I doubt it, but maybe...

Just an aparté : the Amazing Man glitch doesn't teleport NPCs, but their orientation remains South-facing until the START menu is closed.

Je vois que tu es français, ISSOtm, connais-tu PRAMA ? N'hésite pas à venir sur notre forum aussi :) et merci de nous éviter de faire ce test, du coup !

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Re: Pokémon Yellow - easy walk through walls glitch
« Reply #10 on: June 14, 2015, 02:17:56 pm »
I recently bought a Pokémon Rouge (French Red) cartridge, and in this version, this glitch doesn't work along with the Amazing Man glitch (I think there is a link between these). As soon as I enter Pewter City, I get the museum dialog, then the guy teleports away. But as soon as I move, he pops back straight next to the Mart.

I'm going to try entering Pewter City not through the Mart (either re-entering the Safari Zone, then Digging out 1. to Pewter City Pokémon Center or 2. to another Pokémon Center, then entering Pewter city by a) Walking (probably from Viridian City) or b) Flying ; or blacking out)
The glitch does not work on my cartridge. I'm beginning to doubt about this glitch also working on Us carts, that would mean this glitch is emulator-only ? That's sad.

The "Best" result I could achieve was to teleport to Vermilion City, then to fly to Pewter City : the guy began walking downwards as he does infinitely on emulator, but he snapped back towards his normal location after a few steps.

Could someone please test this on a US cartridge ?
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