If you want to run Spiritomb as a speical wall rather than a mixed wall go right ahead, just invest more in SpDef. Spiritomb's defensive stats are completely even though, which is why most people make it a mixed wall. It also can make a solid attacker with the Hypnosis/Nasty Plot set, with no weaknesses it's difficult to OHKO and can hit back harder than more defensive sets. Hope this helped.