Lightning Mastery. One of the 8 available Masteries you can choose from.
Lightning Elemental Mastery allows the ninja to learn Lightning techniques that are high in damage and immobilizing.
Lightning Mastery has some pretty nice benefits to it but like other Masteries it does have its drawbacks as well. The main benefit is its stunning capabilities, while the biggest drawback is the cast times and self-stuns. While the biggest advantage are the stuns, Lightning also has homing techniques available and a gap closer. It is mainly a single target mastery as a lot of the techniques require a target, however some of the techniques have an AoE to them allowing a chance to multi hit targets.
For PvE it's somewhat in the middle as you can kill single target rather easily but it does take quite a while since it's just one at a time however if you play your cards right you will never get hit.
For PvP it's a pretty good mastery in 1v1 but it really shines in group fights as you're given more opportunities to hit enemies with your techniques and providing support in terms of stuns for your other teammates.