What are the real shiny odds in Gen 8 and 9 when taking into consideration the Pokémon Egg Shiny Roll bug?

Question

Possibly stupid question, but bear with me.

I was reading Bulbapedia when I find this interesting little article that implies the Shiny Odds in Gens 8 and 9 may not be what they appear. But I am struggling to understand what it's saying, as I have a peabrain. This is the blurb of text that is confusing me:

however, due to a bug, while breeding the original roll is skipped if any bonus rolls are applied. As a result, the Masuda method has the same probability of producing Shiny Pokémon as it does in Generation VII (both with and without the Shiny Charm); while the Shiny Charm alone actually has a lower chance of producing a Shiny Pokémon than it does in Generation VII or wild encounters do with the Shiny Charm alone.

Can someone please tell me in baby terms what's going on, how it compares to what's intended, and what the odds actually are?

here's another page on the topic, but I am still very confuzzled.

Answer 1

Without the Shiny Charm or Masuda Method, the odds of generating a shiny Egg are 1/4096. In Generations VI and VII, using the Masuda Method adds 5 extra rolls to this, so any given Egg has a 6/4096 of being shiny. The Shiny Charm by itself adds 2 rolls, so the odds become 3/4096. Combining the Masuda Method and Shiny Charm yield odds of 8/4096 for any given Egg.

In Generation VIII, Masuda Method was supposed to provide 6 extra rolls, which would mean odds clock in at 7/4096. The Shiny Charm retained its original 2 extra rolls. However, due to a bug, the initial first roll when generating an Egg is not calculated. This means that...

• The Masuda Method by itself retains its odds from previous generations: 6/4096.
• The Shiny Charm by itself has a lesser impact than it does in previous generations: because the first roll is skipped, the Shiny Charm's odds become 2/4096.
• The Masuda Method and Shiny Charm combined generate the same odds of 8/4096.

This bug carries into Scarlet and Violet.

The short answer is that the Masuda Method, with or without the Shiny Charm, has the same odds as it does in Generations VI and VII. It's only when you have the Shiny Charm by itself that there's a difference: from 3/4096 in VI/VII to 2/4096 in VIII/IX.

Comments

I.e, the devs "intended" to make Masuda Method have an extra shiny roll, but a bug made it so one roll didn't count, leading the odds to be the same as before. I think Game Freak knew of the bug while programming or whatever, and instead of fixing it just added another roll.

Answer 2

To but it briefly, the way the game increases the shiny odds with either the Shiny Charm and/or Masuda method is by rerolling extra personality values, the factor that determines a Pokémon's shininess and a myriad of other things, in an attempt to generate one that results in shininess. Think of it as rolling dice in an attempt to get the same number; the Masuda Method and Shiny Charm simply increase the amount of times you roll the dice!

Now, with the Egg Shiny Roll bug, the initial roll for both the Masuda Method and Shiny Charm aren't factored into the shiny odds when breeding, and only the bonus rerolls for the Personality Values are factored into the shiny odds. This would simply be the same as, say, flipping a coin, then going on to do so three times over for heads, but you only count the extra three rolls, regardless of if the coin landed on heads or not.

The Shiny Charm, just as it had in previous games, is intended to give 2 bonus rolls on top of the initial roll for the personality value for an intended odds of 3/4096 (approximately 1/1365), but as it only factors in the bonus rolls, it instead gives shiny odds of 2/4096 (or 1/2048). The Masuda Method however received an additional bonus roll in Gen 8 and beyond, retaining its old odds of 6/4096 (approximately 1/683), as opposed to its intended odds of 7/4096 (approximately 1/585)

When both are combined, the Masuda Method and Shiny Charm give 8 total rerolls. This results in 8/4096 (or 1/512) odds, although being intended to be 9/4096 (approximately 1/455). Therefore, the Shiny Charm's odds were lowered only when breeding, but thanks to the additional bonus roll, the Masuda Method and the Masuda Method combined with the Shiny Charm retain the same odds as they did in previous Generations.