Manastorm is a NEW unique shield introduced in 3.9 that gives added lightning damage for 4 seconds, based on 25% of your current mana, by sacrificing all of it upon casting any spell. Not many “things” can use this mechanic effectively and i would like to show you one of such setups here. SIRUS 8 down so i can safely say it works and it kills. And it lives too.
https://www.pathofexile.com/forum/view-thread/2777799
