This item is also now available in Besieged. Since the October update, you start out with temporary items (quantity of items varies on the level of the enemy force). It DOUBLES your mp! Absolutely kickass having 2k mp in Besieged. Not sure how long it lasts.
This item is found (or a similar item) when /quarry is used while in ballista. It will boost your MP 25% for 10min~. I may be incorrect on the time and % but its is nice item.