If you want a speedy attacker with deadly power,you could have a shot at Crobat or Xatu.Xatu can learn some really diverse moves and can fly,along with striking quick. Crobat is one of the speediest out there,it can inflict some status conditions like confusion and poison.
Then you could also maybe catch a Gengar,which is also fast and can learn some deadly moves-Destiny Bond,Shadow Ball,Sludge Bomb...
You might also want a strong Heracross,that'll defend the psychic weakness Gengar has. It is offensive and can pack a hard punch.
As for your last one maybe a decent ground or grass type like Sandslash and Vileplume,they make pretty awesome team members :3.hope this helped you out!