What are the odds of getting 2 Masuda Method shinies with HA, same nature, and same gender?

Question

I recently got 2 shiny lapras from the same egg pile. Both are hidden ability (Hydration), Male, and have the Brave nature. What are the odds of that?

Masuda method odds in gen 8 and with the shiny charm are 1/512

The odds of getting a specific nature is 1/25

Lapras’ gender ratio is 50% 50%

And the odds of getting a hidden ability from eggs if the mother has it is 60%

If someone could tell me the odds of that, that would be appreciated

Edit: Also iirc they were hatched 29 eggs apart from each other

Answer 1

Normal Masuda Method shiny odds: 1/512 or 0.1953125%

(1÷512)×(3÷5)×(1÷25)×(1÷2) = 0.0000234375 or 0.00234375% for one Lapras to have each of those specific features you listed, including HA pass down chance, (60/100 or 3/5,) Brave Nature, (1/25,) and Male, (1/2).

Using binomial probability, we can find the odds of finding 2 Lapras with these features in 31 attempts. 0.0000234375 being the chance of an event occurring, 31 being the number of attempts, and 2 being the number of successes, we get 0.00000025525857 or a 0.000025525857% chance. That's 25525857/100 trillion.

I don't really want to do these calculations myself because I know they don't make up a perfect model for Pokemon's RNG...

This number isn't exactly right because of Pokemon's complicated RNG, but it paints a pretty close picture as to how rare this occurrence is.

Comments

This is the probability of finding two consecutive Lapras like this, not the probability of finding two of them within 31 attempts.

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You know how to add that into the formula? I do not.

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It's a question of binomial probability. You need to approach the problem differently.
I don't really want to do these calculations myself because I know they don't make up a perfect model for Pokemon's RNG, which I don't understand deeply enough to give an answer I would be happy with. But OP probably does not care about that.