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Generation I Glitch Discussion

Pokemon Yellow glitch items - Page 1

Pokemon Yellow glitch items

Posted by: rortik
Date: 2015-03-05 13:34:51
After noticing that the data on the big list was not all accurate for Yellow (particularly at larger hex values), and that the list didn't provide data on the effects of activating the items, I decided to test them all out.

I did everything without cheating, through arbitrary code execution, and my findings were…. most of them are useless. The three following effects are (unsurprisingly) the most common:

- Crash the game
- Work as a normal item, like a repel
- Do nothing

There are only a few types of other effects:

- Surfboard (nothing new)
- items like ws m, useable for arbitrary code execution
- lg-, an item with various glitchy effects that does no real harm
- 9F (and various others), an item that forces all NPCs to face downward (or, more likely, simply not update to face the correct direction after two frames onscreen, as they should). Also glitches some sprites. Fixable by talking to any NPC then reloading a map.
- Trade completed! (and various others), a useless item that turns you invisible and lets you get stuck in walls! Yay! (apparently also known as the Jack effect)
- 8F, which warps you to a glitch city like place. However, further movement appears to be impossible.

for a full list of what the items do. Might do Red/Blue next, though I doubt the results will be much different.

Re: Pokemon Yellow glitch items

Posted by: Torchickens
Date: 2015-03-05 14:07:46
Nice work. Notice that items that work like normal items are found at 80h+ and the effect is that item -80h.

The 81h item has Master Ball's effect (item 01), but it is a Super Glitch item so you cannot use it in battle because of its long internal name (more on that below).

94h has the effect of a Potion (hex:14) but using it causes the Rival's effect (also known as the Jack effect) which you describe for "Trade completed!". According to TheZZAZZGlitch, the Rival's effect happens for items that open the party menu but are not included in an internal list of menu opening items. The hex:93 item also causes the Rival's effect, because 93h-80h=13h (Super Potion).

I think you may be mistaken that those are the only effects, because I remember some that warp you to a Glitch City (unless maybe the execution pointer was somewhere in writable memory and you had different data).

Some glitch items (which I nickname "Super Glitch items", luckytyphlosion calls them "TMTRAINER items") have names that have no 50h terminator in the first 20 characters of their name. This causes the data from the buffer $CD6D (which stores the item name in this case) to be copied to $CF4B and onward. There is no 50h so the game copies over 20 characters from that buffer and data from beyond the buffer, which starts with screen data.

With Super Glitch items you can do specific corruptions for specific screen data in Red/Blue or cause the TMTRAINER effect, or cause the Strange Mart glitch (a.k.a. Yami Shop).

Due to the first tile in the cached screen buffer having a 50h in the spot below, if you use those items there you may be able to avoid a few freezes.


An easy way to have an idea of whether something is a Super Glitch item or not is to press A on it in a non-safe spot (with no 50 tile) and see if the game freezes before Use/Toss even appears. However, this is not a true test, because for the Bicycle it doesn't have a Use/Toss box either.

We should also consider that some glitch items may have effects that are while constant, may be very specific/hard to notice or find, like how the hex:7C item in Red/Blue lets you get your Trainer-Fly yield without having to closing the menu (and you can get an infinite chain of encounters with it or by forcing an item to act like it).

Unfortunately with that R/B hex:7C item the game doesn't update CFC4, causing the game to freeze when you run from battle if you have a Trainer-Fly loaded. So you must alter CFC4 manually with a Super Glitch item in a specific spot in Viridian Forest.

Re: Pokemon Yellow glitch items

Posted by: rortik
Date: 2015-03-05 16:14:49
I do remember at least one item that warped me to a glitch city. I think it was 8F. I hadn't recorded it as a separate effect… actually I'm not sure why.

I think because you can't really do anything, so I didn't see it holding any significance. Will edit the OP.