Catch 3 Ditto Pokémon GO is one of the tasks you'll need to complete for the Tricky Pokémon event. Ditto is a rather difficult Pokémon to get your hands on, but here's the easiest way to find them.
Ditto's trademark is that it copies the appearance of other Pokémon. In Pokémon GO, Ditto does not retain its giveaway smiley face when transformed, so you'll only know if you caught Ditto when after you've caught it in disguise.
Catch 3 Ditto Pokémon Go: Ditto's Current Disguises
The Pokémon Ditto can imitate change periodically, so you'll just have to catch every one you see for a chance at Ditto. Here's what Ditto can be disguised as in April 2020.
Just catch three Ditto and you'll complete the task. Ditto will have an increased spawn during the event, so you shouldn't have much trouble getting three of them. Your reward will be an encounter with Croagunk.