Lesser Clarity Potion

Regenerates the Hero's mana by 100 over 30 seconds when used.

Source
These can be bought from Ancients of Wonders in Frozen Throne.

Malfurion, Tyrande, and Maiev can find one in Balancing the Scales, chapter 5 of the Frozen Throne sentinels campaign, Terror of the Tides.

In the RPG
This concoction resembles a clarity potion, but is translucent rather than opaque. It functions like that potion, but for conferring a reduced benefit.