text: h2g2 - A Conversation for Pokemon Go - a Smartphone Game
  A Conversation for Pokemon Go - a Smartphone Game
  Gnomon - time to move on Started conversation Nov 24, 2016
  Ditto is now available; I spotted one in a gym this morning (24th November). It looks like a small, happy, purple blob.
  Rather than repeating what other people say on the net, I'll post details here when I have personally verified them.
  Gnomon - time to move on Posted Nov 25, 2016
  Ditto has the ability to impersonate other Pokémon.
  Catching a Ditto:
  You will encounter a common Pokémon such as a Weedle, Pidgey or Magikarp. When you try to catch it, it looks exactly like what you thought. When you succeed in catching it, it turns into a Ditto, whose CP may be much higher than it was pretending to be.
  For example, the CP10 Magikarp that I caught this morning turned out to be a CP142 Ditto.
  Fighting with a Ditto:
  In a gym battle, a Ditto will impersonate whatever it is fighting against. If you have your Electabuzz up against a Ditto, you'll see the Ditto for about a second and then he will change into an Electabuzz, with all the Electabuzz's attack abilities.