Kaphotics

Should probably upload it. There's also GitHub - projectpokemon/RecoverSaveGen3: Try and recover a Gen3 save file via console app! · GitHub

File size is wrong, not a proper dump. Open it in a hex editor and compare it to another valid save file of the same version to see if it's roughly similar.

Use the encounter database to generate a brand new one.

Duh. To be 100% sure, you'd have to either encounter it without any cheats/shortcuts (e.g. legitimately) or fully understand what is entirely legal on a case-by-case basis, which requires a metric ton of legality/generating knowledge.

The current handler state is not the same as OT/HT trash bytes. Be sure you've not disabled the program Slot Write setting for SetUpdatePKM.

Games across the generations are programmed differently, have different RNG implementations, and different patterns. Gen3 uses a single RNG; a 32-bit Linear Congruential RNG. To simplify things, the 32-bit RNG produces four 16-bit random values to generate the PID (32-bits) and IVs (30 bits). The RNG itself has 2^32 different states, so the PID (2^32) and IVs (2^30) are restricted in the possible results they can be found with. A 32-bit LCRNG cannot output more than 2^32 different combinations; the PID/IV has 2^62 different states possible. Hence, we can check if an RNG seed can yield the current PID/IV through backwards calculation. Gen5 uses two RNG instances to generate a Pokémon. A 32-bit seeded Mersenne Twister generates IVs, and a 64-bit main RNG to produce everything else. The mersenne twister can produce all possible IV combinations, so there is no correlation/restriction to detect for those. The remainder of the "random" properties such as PID-Gender-Ability (32-bits), Nature (0-24) are possible to obtain in any permutation, as the 64-bit RNG is orders of magnitude more random. It is important to note that there are still restrictions; if the game generates things in a specific pattern (like truncating certain bits of the PID) then the Pokémon must still follow the patterns of how the game generates a Pokémon to still be legal. The Entree Forest Pokémon require the ability bitflag of the PID (bit 16) to be 0 so that the game properly remembers it has that ability slot rather than a random ability. If all pkm-property-combinations are randomly possible from the game's RNG, then there is no correlation to detect. It's not worth the time/computation to guess & indicate an RNG seed, when there are billions+ of possible seeds that can originate it.

Use homebrew to properly dump your save data from your 3DS. That file is encrypted.

Oh, I missed the needed move "Wish". I don't see any Gen3 Meowth distributed with Wish. List of Japanese event Pokémon distributions in Generation III - Bulbapedia, the community-driven Pokémon encyclopedia Serebii.net Eventdex - #0052 Meowth

It's there in the encounter database as a Mystery Gift egg Meowth.

An additional caveat for you to consider: just because PKHeX identifies something as "Legal" at this point in time does not mean it is 100% futureproof byte-for-byte equivalent to a legitimate Pokémon. I do not have a list of things that PKHeX does not currently check for. Improvements to checking & generating get added as the years go by, as we identify holes in the checks. So, previously "Legal" Pokémon become detectable as externally modified (e.g. not legitimate). Generally, the official checks per-Pokémon are relatively weak and nowhere near as comprehensive as PKHeX, but again, no guarantees that this will always be the case. It wouldn't be hard for them to task an intern to bulk process an offline database of HOME using PKHeX's API to identify obvious cheaters who are originating the data, or they could task an AI agent to do so as well. It is up to the end user to evaluate the risks of moving externally modified Pokémon through officially monitored systems like HOME. Players have been banned for obvious behaviors like account sharing, repeated trading of clones, and bulk moving of shared databases. They're usually narrowly targeted bans enacted by the developer. We've not seen the massive banwaves of pre-PKHeX-legality-checks in recent years, so maybe they've relented as PKHeX does a good job at dissuading impossible Pokémon.

Generate one from the encounter database then change the SID to shiny using the Alt-Click shortcut for the shinytize button next to the PID.

Issue on GitHub fixed; thanks for reporting. Update Dex on Set doesn't work · Issue #4866 · kwsch/PKHeX

Still not a valid dump. Dunno what to say. The appearance of a save file should not look like that; ORAS save files start off with PokePuff data not a partial section of empty box data. Try a different application like JKSV. Ensure the game actually boots with recognized save data, and that you didn't erroneously restore an incorrect file to the savedata prior to trying to dump.

Not a valid dump; has a ton of sharkive junk at the bottom so it's likely just a bad read (not from the savedata) or something was erroneously restored to it.

Try using a less extreme window scaling setting for your operating system.