I have a skorupi with the nature Jolly.
would it be really fast if I used the nature and EV trained it in speed?
Well, you can get a max Speed stat of 317 with proprer EV training and the like. Jolly is in fact the best nature for the common Drapion.
Jolly adds speed but reduces ur special attack so he'll be very fast even without the ev training
My Drapion is adamant. Which adds attack and reduces Special Attack as it has the Sniper ability so I use Night Slash and Cross Poison which both run off the attack stat. Mine doesnt use any special attacks.