You may need to sit down for this one:
Ditto… Surpassed by Mew in Gen 1 as the top Transformer, didn’t see its golden hour until much later… like 14 years later.
One might have expected Quick Powder (for doubling speed) and Metal Powder (for doubling bulk), to provide it an advantage over Mew in Generation 2, but both were getting rivaled by Spore, Substitute, Thunderwave, Transform Smeargle in Johto’s GSC.
But just like Ditto’s design, the Pokémon itself was finally able to adapt to the situation when it found its place in the meta in Unova‘s BW/B2W2.
A four-generation gap from ”Forgotten” to ”Spoiled Rotton” turned the “anime-good only” meme of 4 generations into the backbone of pure revenge.
And boy, what a difference a clone-of-a-move-into-an-automatic-ability makes.
The surprise-drop (at the time) of the ability, Imposter, came along and gave new life to Ditto, ensuring it could simply pop out into battle, hold Choice Scarf, and punish sweepers with their very own movesets.
It could now check threats that had previously set up, or function as a scout of an entire opponent‘s ability and moveset as a lead, in order to allow you to react accordingly. (Such as switching in a Magic Bouncer if the foe has an Entry Hazard lead that uses Stealth Rocks).
It also served as an ultimate trump card to the weather-war Swift Swim teams that plagued Generation 5. Suddenly, Ditto wasn’t just designed for BW/B2W2, the metagame was designed for Ditto.
Imposter had single-handedly turned seemingly Silly Putty into an improved clone all without any of the item or form change restrictions, of the Pokémon it was turning into might have had.
In its own way, Ditto’s ability to copy an opponent, including Mega forms, was fair: It was a severely limited HP Pokémon, but could come in, copy boosts, abilities, typings and movesets to successfully troll an opponent.
As a side note: Choice Scarf itself deserves an honorable mention for giving Ditto the item necessary for Imposter to be more than a 50% speed—tie gamble.
I dare say: “Ditto improved in a way that hasn’t been seen in any Pokémon since.”
Never has a 1-move, 1-useful-ability Pokemon gone from “Zero”, to “Stop-your-team-from-being-swept Hero”.
It’s ability allows it to now
permanently keep up with the offensive power creep of upcoming generations since it’s debut.
Oh, and that meme of “anime-good only” lasted just long enough for us to realize… That was Pikachu!
As for Ditto? It has the ultimate flex: it is a full blown ”2.0” of your team.