Ninjask

Because Ninjask moves so quickly,  it can become unseeable to others because of its fast movements.  If not trained properly, this Pokemon will refuse to obey its trainer and cry loudly and repetitively.  Hearing this cry for too long can give you a headache.
Bask in the glory of what is probably the fastest Bug-Type Pokemon of all.  It has a base Speed stat of 160.  In battles, you are almost always going to attack first.   However, this high Speed stat comes with a price, as Ninjask has low HP, Defense, Sp. Attack, and Sp. Defense stats.  You have a base Attack stat of 90, which isn't too bad, but it means that you should probably keep a Ninjask Physically based.
For some Physical STAB moves, try giving Ninjask Bug Bite, X-Scissor, or Aerial Ace.  Ninjask has some other good Physical moves, like Slash, Dig, Night Slash, and Giga Impact.  Ninjask does have 1 great strategy.  It can use Baton Pass.  Use it, and you'll switch out Pokemon.  The Pokemon taking the other Pokemon's place has any stat changes made by the user passed down to it.  Let's say Ninjask uses Swords Dance to have its Attack stat highly increased.  If you use Baton Pass after Swords Dance, then the Pokemon taking Ninjask's place will have its Attack stat sharply increased like Ninjask's was.  However, it still doesn't mean Ninjask has the best movepool, but it has some fair options.
Ninjask's ability is called Speed Boost.  Every turn, your Speed stat is increased.  It's not too bad of an ability, but Ninjask is already a ridiculously fast Pokemon, so this ability isn't exactly the most useful one for Ninjask.  This ability is great on other Pokemon, but not so much on Ninjask.
So Ninjask has ups and downs, and will never be the strongest, but I guess it isn't the worst Pokemon out there...