7evy

I don't have any picture/video, but experience does not work properly in double battles : apparently it's distributed at the end of a turn. So if you KO an opponent, then the second KOs one of your mons, all of the experience will go to your only mon left instead of being shared right after you KO the opponent.

A new guy at the Route 3 market sells Gourmet Treats for $650 and buys them for $200... but other vendors still give you $1000 for one, creating infinite money.

Apparently switching when fighting a shadow pokemon skips the opponent's turn. Not sure if this happens for all shadow pokemon, but it definitely does for the shadow Vanillite of Carotos mountain. Edit : not only when switching, sometimes they just don't attack.

When you have more than 70 Zygarde cells, Ayuba (i think that's his name) gives you one lucky egg each time you talk to him, even if he says "come back when you have 100". If you do the Buizel event in East Gearen (battling its former trainer and all) and refuse to take it in your party, "Buizel went off somewhere" but it's still here, and you can talk to it again. The trainer will come back, and you can redo this event indefinitely until you take Buizel with you.