Since the game began, people have been claiming they have caught the elusive Ditto in Pokemon Go, but it wasn't true. Players didn't gain the ability to catch Ditto until mid-November 2016.
Since then, many have found at least on one to add to their Pokedex. If you're one of the players that hasn't gotten your hands on the purple blob, here's everything you need to know.
Finding a Ditto
If you haven't seen a Ditto yet, don't worry. You won't find Ditto lurking around your neighborhood. Ditto hides disguised as other Pokemon and they aren't even uncommon.
Just go about catching Pokemon like normal. When you do catch a Ditto, the Pokeball will stop vibrating and say, "Oh?" Whatever you caught will then transform into a Ditto. Simple.
Dittos hide as Zubats, Pidgeys and Rattatas. Some players are also finding Dittos hiding as Magikarps, too, though it's rare.
Since Ditto could be hiding as anything, your best bet is to catch everything you see, though. I know, catching indiscriminately uses a crapload of balls, but you never know where Ditto will be hiding.
If you like to hunt with friends, there's good news. Once someone around you has discovered a Ditto, he will be revealed to all the trainers in the area. This will probably be your easiest way of finding Ditto. Just hunt around a lot of other people and listen for the call, "I got a Ditto!" By the trainer, there should be a Ditto on the ground ready to be caught.
If you just really don't want to catch common Pokemon, there's one trick that works well for finding hidden Dittos without catching everything. Go to your favorite hunting spot and wait. Commons that don't disappear after a GPS refresh are usually Dittos.
Using a Ditto
Taking Ditto to the gym to battle or train is a little different than with other Pokemon. Ditto only has one main move and that is to transform. So, when you put in him in battle, that's exactly what he does. He transforms into the first Pokemon he sees, which is whatever it is battling. Once your Ditto has transformed, it stays in that form for the entire battle.
Even though it transforms into the Pokemon it's battling and uses it's move, it doesn't take on the CP and stats. Though the CP and stats adjust, somewhat, they don't always match what you're battling. So, make sure you have a tough Ditto before trying to beat a gym with it.
Also, it takes a few seconds for Ditto to transform. This can take valuable time away from your fight, particularly if you are a trainer who likes to dodge the first couple of hits to get an advantage.
If a Ditto encounters another Ditto, the resulting fight is a little different. I haven't seen this happen myself, but this video posted by WhatUpMC (around the 3:34 mark) shows that the two Dittos will just wiggle around until the secondary move, Struggle, is used. Eventually, one of the Dittos will win the fight.