These spectres use lightning version of firestorm on 4 sec cd and 3 sec duration, they use melee attack when spell in on cd. They are on the slower side of map clearing, but they have good single target dmg with 18 lightning storms on single target with my current setup, i tried them on Maven and they shredded hp pretty fast, didn't record it cuz of my embarrassing bossing skills :)

My glass cannon PoB: https://pobb.in/9l2VudRj3kjT

https://poedb.tw/us/Charged_Colossus_

Get them form T17 map or by taking Invasive Adversaries node on Atlas tree, then spam white maps and just desecrate.