Overcharge

Overcharged ~, Level 1
Overcharging an ability raises its cost by 10%.

It does allow you to cast it, even if you are not able to pay the mana costs.

Your mp will stick at 0 for an amount of minutes equal to the amount of mp you were lacking when activating the modified skill.

Note: You can only use overcharged ~ while you have at least 1mp.

Overcharge - Lv. 1
Passive

Hold (Skill Level x10)% mp in excess of maximum without consequence for one hour. Unused excess mp may be relinquished at the end of the duration. Exceeding the limitations of Overcharge subjects the user to Mana Shock as per normal.

Hidden Mechanics (Item)
How Overcharge Works:

The extra 10% storage does not fill naturally, the mana must be drawn from an external source.

By default, excess mana will shunt out after one hour unless John willingly keeps it in.

If John goes over 110% storage, or keeps the extra 10% longer than one hour, he suffers Mana Shock like anyone else.