|Giant Chasm (Forest)||8 Badges|
Who's that Pokemon? It's Pikachu! Oh wait, no, it's just a Ditto. Ditto is a Normal-type Pokemon that lives to transform into other Pokemon. Its stats are pure rubbish, having absolutely terrible everything. Its ability is garbage: Limber, which just prevents it from being paralyzed. You can very rarely find a Ditto with its Hidden Ability inside of the Hidden Grotto in the area (after you clear the Plasma Frigate), and that ability is Impostor, which allows it to transform into the foe immediately when it is sent out, plus you copy its stat changes as well. That's rather helpful, but it's still a pain to get and not really worth it in-game unless you're using a Choice Scarf or something, which isn't really the easiest thing to get.
For moves, Ditto knows just one move: Transform, which transforms it into the foe, copying its stats (other than HP), type, and moves, although all moves have only 5 PP. Ditto's HP is really, really low, and it'll have to survive an attack just to copy the foe. Why would you ever bother doing that? It's terrible.
TM moves? Move Tutor moves? Ditto asks, "What are those?" as it stares at you blankly. Yeah. Transform is literally the ONLY move it can ever learn.
You would be better off using any other half-star Pokemon than you would Ditto. It's just so bad (outside of the competitive Choice Scarf Impostor version, which is only useful if you know what you're doing) that it isn't worth the Poke Ball you'll use to catch it. The only redeeming factor is it is very helpful for breeding, as it is capable of breeding with any Pokemon not in the No Eggs group, so it can breed with males, females, and even certain genderless Pokemon to get you eggs — although the Pokemon Day-Care isn't even available until after beating the game, so it won't do you much good immediately anyway.