What is the problem with this Mewtwo?

Question

Aparrently there is a problem with this Pokémon.

Mewtwo@Life Orb
Transferred from Gen 1 VC Blue
Moves:
—Selfdestruct
—Reflect
—Trick Room
—Light Screen
TID:12345 SID:00000
OT: BenLaden
Shiny: Yes
31*6 Ivs
Symbol type: Game boy symbol
Ribbons: None

Something about this is wrong.

Also I’m not sure if this is correlated with my other Gen 1 pokes not working.

Comments

Gen 1 doesn't work with pokemon bank I believe. Try poketransfer.

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Im trying to store it in the poke bank. It’s hacked it to ultra sun.

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Hasn't it been established that Pokebank has a hack check?

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I’m pretty sure the OT name can’t be 8 characters long in Gen 1. I know Gen 4 only allows 7 characters for your trainer name, and I don’t think Gen 4 would have less character slots than Gen 1. I could be wrong about that, though, and that’s an obscure enough detail that I wouldn’t be overly surprised if Pokébank’s hack check doesn’t even look for that.

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Yo. I think that solved the problem.

Btw it’s not pokebank hack check I was talking about it was PKHeX.

Answer 1

Here is the problem:
Pokemon transferred through the Poke Transporter from the Gen 1 virtual console releases will only be shiny when transferred to Sun/Moon if they have a specific set of IVs:

The method to determine whether a Pokémon will be Shiny has varied:
In version 1.3, a transferred Pokémon will be Shiny if in Generation I its Speed, Defense, and Special IVs are all 10, and its Attack IV is 2, 3, 6, 7, 10, 11, 14 or 15. This is the method used to determine whether a Pokémon is Shiny in Generation II. If it does not meet these requirements, it will never be Shiny.
Source

This Mewtwo is hacked, and it was never transferred from a virtual console game in the first place. If you receive a shiny legendary with all perfect stats, that’s an immediate red flag.

Someone also pointed out in the comments that it has an OT that’s one character longer than the limit in the Gen 1 games, which is likely another issue the hack checker found with it.

Comments

The OT was the problem, however you just pointed out an oversight in PKHeX. Nice!

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Oh I don’t think I read all of the comments and assumed it was already in your game. Well anyway, hopefully it’ll be treated as legal after you change the OT

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When you send a VC Pokemon through Transporter, its old IVs are ignored for all purposes except gender/shiny/Unown shape, and replaced with a new set that uses the modern structure (so 6 independently controlled stats instead of just 4, and each one has twice the precision) and a guarantee that at least three of those stats will be maxed out. The IVs it has after transfer bear no relation to what it might have had before, and this is not an inconsistency (at least not for a static encounter like Mewtwo).

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Oops that was a pretty big oversight on my part.