As of October 2023, Ditto can be disguised as the following Pokémon in Pokémon Go:

• Diglett (Gen 1, Kanto)
• Grimer (Gen 1, Kanto)
• Snubbull (Gen 2, Johto)
• Corphish (Gen 3, Hoenn)
• Starly (Gen 4, Sinnoh)
• Roggenrola (Gen 5, Unova)
• Tympole (Gen 5, Unova)
• Litleo (Gen 6, Kalos)

Its important to note that Dittos disguises can change from time to time, so its best to keep up to date with the current disguises if youre trying to catch one. Additionally, Ditto will never appear as a Ditto on the overworld map, so players will need to catch one of the disguised Pokémon to find out if its a Ditto in disguise.