<p>Ditto has always been deemed a gimmick, even. The poor little blob  has been around since its RBY days, and it was never used. The same went for the  start of Generation V, and where the same old Ditto was never competetively viable still not viable in  any tier, not even NU. Then came the shift to BW2, and with it came a  new ability for Ditto, a saving grace that would bring him it right out  from the lowest depths of NU:(colon) Ditto obtained Imposter.(stop) Imposter an ability that  essentially uses the move transforms Ditto upon switch in, rather than having  to take a turn using it wasting a turn it. This ability is what took transformed Ditto from a useless  gimmick into a ruthless revenge killer. It Ditto is a setup sweeper's worst  nightmare, and when equipped with a Choice Scarf, Ditto it can outspeed and  kill almost everything in UU, provided that it can switch in with  minimal damage.</p> 
[SET]
name: REVENGE!
move 1: Transform
move 2: None
Move 3: None
Move 4: None
Item: Choice Scarf
Ability: Imposter
Nature: Sassy
ivs: 30 SpA / 30 SpD / 3 Spe
evs: 252 HP / 4 Def / 252 SpD
[SET COMMENTS]
<p>As ifTaking revenge on anyone who ever deemed him it useless,  Ditto takes its new Dream world ability to become a potent revenge  killer. Armed with a Choice Scarf, Ditto can come in, outspeed, and kill  almost anything, bar Substitute users and Zoroark. Any boosting sweeper  must think twice if they see Ditto on the opposing team, because after  they grab some boosts and a kill, Ditto can come in and not only pocket a  revenge kill, but also steal the boost and turn the sweep around. For  example, Ditto can steal boosts from the likes of Pokemon like Dragon Dance Kingdra, Dragon DanceScrafty, Swords Dance Heracross, Nasty Plot Houndoom,  and Nasty Plot Azelf, even after a single kill. are just a few of the Pokemon that Ditto can easily steal  boosts from after a single kill. Its killing abilities don't sweeping potential doesn't stop there—(dash)Ditto can switch in and murder all kinds of threaten a range of LO attackers, or  virtually any Pokemon that doesn't have a heavy reliance on their item  and a move they can kill themselves with.(I'm confused by this, are you trying to say "Pokemon that have a heavy reliance on their item and a move they can kill themselves with"?) Not only does Ditto have great Outside of its revenge killing capabilities, but it also has the ability to Ditto can also steal entry  hazards and further support moves from the opponent. Ditto can come in on switch into the likes of Bronzong,  Gligar, Swampert, or even and Roserade,(comma) and set up Stealth Rock or Spikes—(dash)although this requires Ditto to be locks Ditto into a hazard move, it can  prove to be incredibly useful in the long run. This is obviously the only moveset that  Ditto can run, as its movepool is limited to one move. being said ,but  Ditto doesn't need to worry about its own movepool because it will be  using someone else's moves nearly all of the time anyway.</p>
[ADDITIONAL COMMENTS]
<p>Since Ditto copies the stats (bar HP) from the its opponent, it  seems odd to have this put much thought put into EV and IV spreads. They do  have a purpose, however, even if it is small. as HP is the only stat not  copied when Imposter takes effect, thus EVs in that stat are maxed out.  The rest of the remaining EVs only matter in for one situation:(colon) Ditto switching in  on Zoroark. Although this should never happen, Ditto still wants to have  maxed Special Defense to try and in case it needs to take a hit. However, if this does  happen, Ditto is pretty much out of luck. The only effect of Ditto's IVs  after Imposter takes effect is the type of its Hidden Power. This IV  spread is chosen because it changes Hidden Power to a Ground-type move.  This is useful in UU because there are two main users of Hidden Power:(colon)  Raikou and Zapdos. Hidden Power Ground is Ditto's only way of getting past Raikou,  and Zapdos is hit harder by its own Thunderbolt than any type of Hidden  Power. 3 Speed EVs are a given to ensure chosen because it keeps the Base Power of Hidden  Power at is 70, while obtaining the lowest Speed possible. This is done  for the only situation it could effect, Ditto vs. Ditto. In this  situation, the faster Ditto loses because it runs out of PP first. Sassy  is the nature of choice because it makes Ditto even slower, and helps  Ditto take a hit from Zoroark. As for teammates, Ditto doesn't affect  a team’s synergy, thus its team options are extremely varied. Any team that  enjoys having a good revenge killer; is having trouble with setup  sweepers; and has a free spot synergy wise;(semi) Ditto is a good teammate.  Also, because of Ditto's ability to transform into the opponent's  Stealth Rock user, it can usually eliminates the need for a Stealth Rock user of your  own. This can be a great help to free up team slots.</p>
[Other Options]
<p>Ditto basically has no other options other than the above set.  The only aspect worth changing would be the IV spread, which helps to  target different users of Hidden Power on the switch in. Below is a list  of Hidden Power users and the best IV spreads for beating them</p>
<ul>
<li>-Raikou: 31 HP / 31 Atk / 31 Def / 30 SpA / 30 SpD / 3 Spe [Lowest Speed  Possible w/ Base 70] HP Ground (51.71 - 61.05%) -- guaranteed 2HKO</li>
<li>-Zapdos: N/A, Thunderbolt (66.66 - 78.5%) -- guaranteed 2HKO (Hits for the same damage as HP Ice/Rock)</li>
<li>-Lilligant: 31 HP / 31 Atk / 31 Def / 31 SpA / 31 SpD / 2 Spe [Lowest  Speed Possible w/ Base 70] HP Ice (87.23 - 102.83%) -- 18.75% chance to  OHKO</li>
<li>-Shaymin: (Air Slash is more common than Hidden Power) 31 HP / 31 Atk /  31 Def / 31 SpA / 31 SpD / 2 Spe [Lowest Speed Possible w/ Base 70] HP  Ice (48.53 - 57.3%) -- 94.14% chance to 2HKO</li>
</ul>
<p>Therefore, The above IV Spread for Hidden Power Ice is probably the best  alternative to use if your team is more worried about revenge killing  Lilligant and Shaymin than Raikou. That being said, Raikou is much more  commonly seen with Hidden Power than the Grass Duo, so Hidden Power Ground is  probably the best way to go. Theoretically, the item on the set could be  changed, but it is usually ineffective to do so because Ditto will  always be relying on a speed tie, and outright losing to Choice Scarf  users.</p>
[Checks and Counters]
<p>Because Ditto is ever-changing, there is no true counter to it.  Scarf users are probably the biggest check because Ditto relies on  being faster than the opponent to get a revenge kill;(semi) and Choice Scarf  users will always create a speed tie, only allowing Ditto to do its job  50% of the time. As Imposter will not work fail if the opponent has a  substitute, making users of said move are obvious checks;(Semi) but only if of course, the Substitute must be was set up before Ditto switches in. If not, Ditto can just outspeed and attack before the move is used. Ditto is also largely  susceptible to entry hazards, especially Toxic Spikes. Ditto will be  switching in and out a lot, and thus taking lots of entry hazard damage.  This makes Ditto slightly less effective against teams that stack entry  hazards.</p>