The blue pentagon on the status screen, so far every Pokemon in X and Y has one but Pokemon transferred from Black/White/Black 2/White 2 won't.
Initially people erroneously thought it had something to do with hack detection. Stating that if it wasn't there the Pokemon is hacked.
This was partially based on the fact that Pokemon without the mark are banned from an upcoming tournament (even though they probably won't be banned from future tournaments).
NIntendo/GameFreak has always been known to run specific generation tournaments. I'd imagine this IS the case. The pentagon probably has nothing to do with hacked pokemon, and even if it did, hacked pokemon are undetecable from legit pokemon when done right, so they would bear the pentagon or not bear it just the same as any legit one... and when hacking reaches a more public light in Gen 6.. it would be pretty easy to just hack the pentagon onto the pokemon. Although if it is a Kalos-region only mark, then pokemon not native to Kalos bearing the mark would a sign of poor hacking (like if someone did it to, say... a Heatran, or Arceus)
Kalos Native Pokémon used in the Standard Format must be native to the Kalos region in Pokémon X or Pokémon Y. A native Pokémon is a Pokémon that is hatched or caught in Pokémon X or Pokémon Y. Pokémon that have been transferred to Pokémon X or Pokémon Y via Pokémon Bank or Poké Transporter are not native.
Taken from the official rules on Pokemon.com
Although the tournament prevents you from using Pokemon transferred from previous gens, the rules allow you to use these Pokemon for breeding. You are however restricted to using only Pokemon found in the 3 Kalos dexes (except for Xerneas, Yveltal, Zygarde, and Mewtwo).
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