curious why do you use horror instead of wall of fire? WoF is superior in every way, and you can already use it from relatively early to mid game. other then that looks great, though chain lightning seems imo better early-mid game and in later game you have better options, I ran it before a lot, I now prefer Wall of Flame. (like WoF+Fire Mine/ Immolate). I personally think the most damage in the shortest time on necro one would theoretically get with the free walking bomb+EB, but also add to that chaotic focus enhanced fire mine, of course at that point you would have to be lvl 18+ and have used a few amulets of power for some extra ability points.
Well this build was mainly around a Lightning/Necromacer build, and i have so many more lined up that just like you others have commented to me, and what they say are just builds i have lined up for more future videos, and now going on to be level 22 on my main i have some new better builds i can get out that do so much damage
just have to wait for them to come out as i only have time currently for 1 video every two weeks but close to june i will be able to increase that as exam with be over, YES!!!! xD but back to mages, there are more builds that do more damage that i will make, and some require synergy from companions some dont but i know you'll like what i have lined up for the future as builds i have worked on and tried to calculate damage, well too much damage to calculate xD Hope you enjoy them and also i think the best build is the one you prefer and find fun, its like that for most games, the more fun you have with a build and the more you prefer it the more likely you'll just do more damage with it, so i mainly make build video to give ideas so that you can develop them to your liking.
Happy Adventuring