This is probably the fastest TX13 build for Necro, capable of doing 2 min T13 runs on a regular basis (and certainly sub 2min with decent density or pylon luck). And it's also super easy to play like LazyNecro should be played. Can be also used for bounties (except Belial bounty, more info down in the comments), then i recommend Warzenian bracers instead of Nemesis.
It does not require any CDR or RCR or hitting any breakpoints, there's no timing skills or numlocking anything. just move and monsters die by itself. It's damage output is very much linear as your gearing is progressed, as long as you have main items.
If you have mousewheel that you can click, then you don't need the keyboard at all to play. You move with holding LMB, fire occasional Bone Armor with RMB and blood rush with mousewheel click.
LotD and Simulacrum are occasional and only real use for Rift Guardian. just pop them for pretty much instakill, especially if you catch Physical CoE phase. You can even use manual cast with just clicking these two skills on your hotbar with your mouse.
NB! aura on Left mouse button is imporant, as these skills are not "clickable" and therefore game takes it like Force Move action.
For clarifications: how this build works.
- If you have at least one stack of Bone Armor active with Inarius 6-piece set bonus, you'll gain 15 yard radius autodamage aura. If you start dealing damage within 15 yard (the tornado range), all this damage will be increased by 3500% (I6 bonus) and you'll keep damage bonus on Damage over Tme effects even if monsters leave your tornado range for 3 seconds
The aura itself does little damage (doesn't get benefits from 6pc Inarius bonus itself!). Also, refreshing Bone Armor itself too often is not that important, as it's damage is not too great, so any Bone Armor Skill bonus is pretty much a wasted stat. Of course you want to have max 15 stacks (pretty much given, if you're bit careful from the start), because you'll get much higher damage reduction from Wisdom of Kalan amulet and little bit bonus movespeed too.
- autodamage applies your Damage of Time effects: Toxin gem and can (if it crits) apply Pain Enhancer gem (which is major part of the damage output). It's really important to stack critical hit chance to have higher chance to apply PE.
- Your Aura of Frailty will apply autocurse for every enemy within 15 yards (besides killing anything below 15% HP). This will give you damage bonus for Trag'oul Fang and damage reduction for Dayntee's belt. Eternal Torment passive ensures that any monster you curse, will stay Frailty cursed for at least around 3 screen range.
- cold runed Bone Armor will apply slow with Lost Time offhand (in addition to provide movespeed bonus) and this ensures Bane of the Trapped and Kyrsbin 100% bonud damage even outside BoTT radius
So TL;DR, you move through any mob, the get cursed (Fang, Daintees), slowed (Lost Time) for complete BoTT gem uptime and Krysbin first part (100% dam increase), applied DoT-s to them (PE/Toxin) and all this DoT damage gets multiplied by other factors (reilena's, other skills, pylons etc). For RG-s you can add simulacrum (double damage with Reilena's as it'll double your Essence pool) and full krysbin (300%) with Land of the Dead. You'll get some full 300% Krysbin thorough the rifts too (from enchantress and speed pylon for example), but it's not that reliable. Also, with autoconsume from Devour/fueled by death and autoslow from lost time you'll get tons of movespeed. And then you add steuart boots for insane movespeed.
And that's it, you dont cast any skills (except Bone Armor refresh) manually, you just move through mobs and you deal automatic passive, aura-like damage. Damage that's greatly amplified multiple damage bonuses (6pc set, BoTT, krysbin, fang, reliena, CoE, etc).
This is not a GR pushing build and will probably hit a wall at high 80-s (i remember doing a GR83 at about 7:30), but it's very handy TX13, bounties and gem-ups, especially as this is very smooth and "relaxing" build.
* level up your Pain Enhancer as high as possible. This is majority of the damage.
* if you feel your elitekilling is a bit slow, swap Simulacrum (it's occasional anyway) for Bone Spirit (Possession rune is best for meaty Krysbin 300% bonus), but it'll make your gameplay a bit less lazy and adds a bit of "mashing". Bone Spirit has greaty synergy with autodevour, so you'll have plenty of charges.
* you're most vulnerable at the start, where your Bone Armor stacks haven't yet reached 15 stacks. You can start your rift with enabling Land of the Dead and gathering some "free" stacks while others are frozen. If you don't want to waste LotD, then Blood Rush into the middle of the biggest pack and activate Bone armor ASAP (Potency gives you ton of armor for short time too)
* Don't STOP. as simple as that, you don't need to stop other than picking up items (Death Breaths, legendaries, mats). The more you move, the less damage you'll take.