If you want a Physical passer go with
Nature: Jolly or Adamant
EVs: 252 Def, 252 Sp. Def, 4HP
If you want a special passer go with
Nature: Modest or Timid
EVs: 252 Speed, 126 Def/Sp.Def, and 4HP
I use ninjask as a passer, usually sending him in after setting up light screen and reflect, he is fantastic. Don't go with DW abilitys, their normal ones will work better.