Here I am going to try and answer for you, with what other trainers have experinced while using or confronting Ditto in gyms.
Now this is probably why Niantic took so long to add Ditto into the game, its confusions like what does Ditto transform into if it is defending a gym and there are two attackers? What happens when Ditto fights Ditto? What happens when a trainer enters a battle with a Ditto while another battle with a different Pokémon is taking place?
Well here I am going to try and answer for you, with what other trainers have experinced while using or confronting Ditto in gyms.
First of all as I explained in another article earlier this week, when Ditto fights Ditto nothing happens and they both just simply don’t transform.
But as for the other question many Pokémon Go players have asked about, what happens when Ditto is defending and there are two trainers trying to capture the gym? Well then obviously Ditto transforms.
But which one does Ditto transform into? Well through observations sourced from trainers on a number of forums, it picks the weaker Pokémon to transform into.
There was a case where a two trainers, one with a Vaporeon and the other with a Rhydon attempted to take down a gym with a defending Ditto. The Ditto decided to chose the Rydon to transform into despite, the Vaporeon being stronger.
But this doesn’t seem to be a one off instance, as a number of players have also stated that this has too happened to them.
I assume this is that case because if a low level player was to try and take over the gym alongside a high level player, then the Ditto would destroy the low level player as even if Ditto was weak, as it would take the traits of the stronger Pokemon.
But this also may work in favour of team battles in general as one player could enter a gym with a strong Snorlax, while the other could enter it with a Rattata and so have the Ditto transform into the weaker Rattata.
Also another thing to take into account if you are attacking a gym with a Ditto, it seems as if that it only Transforms once even if you win and go over to the next Pokémon.
So there you have it, I hope that answered some questions about battling Ditto in gyms with a teammate, as there were so many unanswered questions about Ditto earlier this week.