Greased Lightning is Yuffie's first level 1 Limit in Final Fantasy VII, available to her by default. It is a physical attack on a single target that strikes for 3.125 times her normal damage. Using Greased Lightning eight times unlocks Yuffie's second level 1 Limit, Clear Tranquil.
Greased Lightning is performed by Yuffie dashing at an enemy and striking hard with her equipped weapon.
Greased Lightning is a simple physical attack that deals 3.125 times Yuffie's physical damage. As such, its damage is determined by Yuffie's Strength stat and her currently equipped weapon. Yuffie has average Strength and her stats are middle-of-the-road, meaning her damage with Greased Lightning may be slightly lower than other characters' comparable level 1 Limit Breaks can manage.
After using Greased Lightning, Yuffie will unlock Clear Tranquil. Clear Tranquil can be a very effective healing ability throughout much of the game, meaning some players may wish to leave Yuffie in level 1 and also retain access to Greased Lightning. Clear Tranquil is the superior ability, though Greased Lightning provides an effective way to deal a quick burst of damage if the party does not need healing, as level 1 Limits charge much faster later in the game. It can be a good idea to leave Yuffie for Level 1 Limit Level for her sidequest in the Pagoda in Wutai Village and use Clear Tranquil to heal, and Greased Lightning to defeat an enemy if it is within the threshold. This can also work for the Battle Square.