Dry underflow glitch is a glitch in Pokémon Red, Blue, Yellow and a major sub-glitch of having a x255 item stack.
It was documented by luckytyphlosion (thread).
It is a better method because it doesn't require the Saffron guards to be thirsty or a Fossil. It relies on an oversight in an in-game mechanic which allows the player to merge two item stacks (e.g. Ultra Ball x1, Ultra Ball x20) of the same kind into one stack, by swapping them.
Also, it can be done with the PC items, allowing one to edit more RAM addresses that could only be manipulated with arbitrary code execution or map FE.
You will need 2 different tossable items, and a stack of 255 items.
Refer to below for methods of obtaining a x255 item quantity slot for this glitch:
- Order your items so that your 2 tossable items are in slots 1 and 2 and the item x255 is in slot 3.
- Toss everything below the item x255.
- Toss the top two items so you have three items x255 (item count=1)
- Toss 253 of the first item x255.
- Swap item 1 with item 2.
- Swap item 1 with item 2, again.
You can also do this with items below the third (and initial) 255 stack. You need to count how many items you have, then after step 3 toss the top item x255 the number of items you initially had -2.
Methods to obtain x255 stack
1) Encounter a MissingNo. (e.g. with old man glitch, Trainer escape glitch, CoolTrainer♀ glitch) to add 128 to the sixth item quantity (if less than 127).
For Pokémon Yellow:
Unstable MissingNo. will not freeze the game if encountered for the first time after a wiped save file with Up+Select+B and if no other glitch Pokémon sprite was viewed. More reliably, the double Trainer escape glitch with Level 80 Starmie can be used (video) to encounter a Fossil/Ghost MissingNo., which will not freeze the game. Alternatively though more difficult, the player may perform the Ditto glitch sub-glitch of the Trainer escape glitch by having Ditto Transform into a Pokémon with 182, 183, 184 Special.
2) Either encounter MissingNo. again or catch it with the sixth item quantity as x127 to get the x255 stack. Note this will not work when catching the MissingNo. if the item used to catch it was the sixth and a Poké Ball x127, therefore items like X Special are more desirable (also in this case, because X Special can be used for Celadon looping map glitch)