They finally released Ditto in Pokemon Go after how much of a wait! You wouldn’t know you had caught Ditto until after you’ve caught the Pokemon it transformed itself into. So if you caught some lame common Pokemon like a Pidgey, it would end up showing up as a Ditto after you’ve captured it.
Before the only way to get Ditto was by actually hacking the game but this was only through versions of the game that have been cracked. If you tried connecting to the servers with it, it would not work at all. Unless you use a Pokemon Go hack that actually can bypass this. Ditto was already built into the game, it was just never actually officially released, if Niantic caught you with a Ditto in your account it would be taken away a soft ban would be placed on your account.
The Dittos that have been caught usually have a high CP and people have been telling us that they can be caught in every region. One key attack that Ditto has always had and only has is transform and it is going to get that move in the game. Now battling Gyms will be a lot more interesting with two of the same Pokemon battling each other, maybe whoever has the higher CP will determine the victor!
If you put Ditto in a gym it will take the appearance of whatever Pokemon you use to battle it. Be prepared for long ineffective battles against each other. Your best bet is to always have a friend with you battling the gym with Pokemon that counter the six that you’re carrying with you into the fight.