In addition to its defensive bonuses, it provides a 12% reduction to damage from creatures and players in TzHaar City.
With an update on the 30th April 2013, the armour no longer triples damage taken by you when fighting in PvP or any other monster.
When used with the rest of the obsidian armour and either an melee, ranged or magic helmet, it will increase your accuracy by 10%, very similar to the Void Knight equipment.
The Obsidian plateskirt degrades after 4000 hits. Once it fully degrades it cannot be reused, and a new plateskirt must be smithed.