This is a solo abom build.
You use the skeletons/mages as feed for a non decaying abom.
You buff it with infernal shade and dreadshade to give it lots of speed/100% crit chance and tons and tons of damage.
The abom is melee, and has okayish melee hit aoe. but what makes it really strong is you are able to invest everything into defense. the abom scales it self pretty much. just getting int is enough it gets bonkers levels of more multipliers in its tree.
This is why the build uses a chronostasis. it comes with ward per second in the main hand slot which is unique to it.
He is using plague minion idols because aboms plague will do tons of aoe damage because he has like I said, bonkers levels of more multipliers that apply to him globally.
Abom needs no real minion health scaling he gets the total health of the minions that make him up, and then 10% per player level. He is unkillable with decent leech which he gets thanks to necro tree.
All his gear is invested into getting more ward from his low life items, more ward retention thanks to cold res, and more int for some damage and even more ward retention. as well as some flat ward per second on his offhand/mainhand.
The build is decent at pushing corruption as well, but clears monos very slow vs other builds, but its fine for arena as arena is all about staying alive and not exactly about time efficiency.
This is the current necro strat imo. Most necros for ladder seem to run either wraithlord who you build pretty much the same as abom, get the wraithlord, as many more multis as you can, and buff him with solo shades.
You can also do a similar build with archmage, but I think wraithlord has consumed that build since its just archmage but better.
edit: as of typing this, a wraithlord build has passed the abom guy. but they have very similar gearing ideas.