(Copied and pasted from Suggestions as suggested)
[Note: The person who told me about is mechanic is
Enigami, he knows more than me and might be able to fill in the exact mechanics that'd need to be known to implement properly]
In Gen 1, to prevent the games from desyncing on a link battle, the game pre-generates numbers for the first 10 RNG rolls. However, the game only generates values from 0-252 rather than 0-255 for these rolls. This effects every RNG related mechanic before the first 10 RNG rolls are used up, including accuracy, secondary effect chance, crit chance, damage rolls, and even speed ties. The bug here of course being that PS does not simulate this, all rolls are 0-255.
Examples of effects on gameplay:
-Just about every effect becomes more likely, since typically RNG rolls look for X number or lower to take into effect. This also means you cannot 1/256 miss in the first 10 RNG rolls, as that happens when you roll a 255 for accuracy.
-Jynx's Lovely Kiss has a 191/256 (~74.6%) chance to land normally, but if in the first 10 RNG rolls, it has a 191/253 (~75.5%) chance instead. Blizzard has 230/253 (~90.9%) accuracy and a 26/253 (~10.3%) chance to freeze if it hits.
-If Alakazam uses Psychic, the game does a total of 4 RNG rolls for: Accuracy, Damage, Critical hit, Special drop. Add another for full paralyses and speed ties if they apply.
-Player 1 wins speed ties if the roll is 0-127, player 2 wins if the roll is 128-255. If the maximum roll is 252 instead the odds change to 128/253 (~50.6%) for player 1 and 126/253 (~49.4%) for player 2.
Note: All of this occurs
only within the first 10 RNG rolls, after these rolls all rolls become the standard 0-255.
A few things need to be checked to implement properly such as: Is the player this increases the speed tie chance for consistent? (ie: Is it always the host?) What order do RNG rolls occur? (If there are 2 remaining RNG rolls and Alakazam uses Psychic, which RNG rolls get changed odds?) And just general verification of the mechanic itself.
edit: Looking back on the chat, Enigami seems to say the order is: Accuracy, Critical Hit, Secondary Effect, Damage roll; and that under certain circumstances damage roll may use 2 rolls. Still worth verifying all this on cart to ensure proper implementation.