HGSS Bug-Catching Contest Cute Charm RNG

[pokeknight]

Playing around with Cute Charm RNG for a Scyther with the following spread in HeartGold:

 

The latest version of PKHeX marks the above 31/31/31/21/31/31/31 Adamant spread as illegal, not able to find a matching RNG frame despite correctly detecting the Cute Charm PID type. I recall that an older version of PKHeX allowed any combination of Cute Charm PID-IV, so is the new legality checker just overzealous? I've attached a mockup of the target Scizor- what am I missing, or is this a bug?

0212 - SCIZOR - EA3200000099.pk4

[Kaphotics]

1 hour ago, pokeknight said:

what am I missing

If you're running a Cute Charm lead, how do you trigger the encounter? There are no species that have the ability Cute Charm, that can also learn Sweet Scent.

Without Sweet Scent, you must "randomly" encounter it. That is why PKHeX flags it; you cannot trigger an encounter to land on that PID/IV -- RNG Reporter does not check if a lead can exist for it. The "random" chance of triggering the encounter is 25% (boosting to ~37% via White Flute).

See below snippets of PKHeX's code where it verifies the feasibility of "random" encounters.

    private static bool IsAbleToSweetScent(this LeadRequired lead) => lead
        is None // Pretty much anything grass.
        or IntimidateKeenEyeFail // Masquerain & Mawile
        or PressureHustleSpirit or PressureHustleSpiritFail // Vespiquen
        // Synchronize: None
        // Cute Charm: None
        // Static/Magnet Pull: None
    ;


        // BCC only allows one Pokémon to be in the party.
        // Specific lead abilities can learn Sweet Scent, while others cannot.
        // The only entry into this method requires an ability that has no species available with Sweet Scent.
        // Therefore, without Sweet Scent, we need to trigger via turning/walking.
        // With an area rate of 25, this arrangement will succeed 37% of the time.

        // The game checks 2 random calls to trigger the encounter: movement -> rate -> generate.
        // HG/SS has an underflow error (via radio) which can pass the first rand call for movement.
        // Only need to check the second call for rate.
        // Rate can be improved by 50% if the White Flute is used.
        // Other abilities can also affect the rate, but we can't use them with our current lead.

 

[pokeknight]

Thanks for replying! If this is technically possible albeit unlikely (~37%) assuming every other RNG step was correctly hit, shouldn't PKHeX mark the resulting Scyther as Fishy instead of Illegal?

[Kaphotics]

16 minutes ago, pokeknight said:

Thanks for replying! If this is technically possible albeit unlikely (~37%) assuming every other RNG step was correctly hit, shouldn't PKHeX mark the resulting Scyther as Fishy instead of Illegal?

PKHeX is telling you that there is no RNG frame that can hit the seed, because it checked every single frame against that 37%. It's an impossible-to-hit frame, aka illegal.