This build is a very fun build that you can tweak and make your own. I see a lot of potential in it, but I don't have the gear to test how far it can go.
Nonetheless, I can safely say with under 600 paragon and no ancients that I carry 4 man GR60's with this build. I run this build in T13 rifts as well with some minor tweaks but my Lawnmower build is much faster. I still play this one because I feel more engaged in fights.
The damage for this build revolves around item procs and poisons. You must have 3 stacks of Nayr's Black Death at all times which is very easy. Once you gain 3 stacks, it usually stays at 3 stacks for the entire rift.
How to play?
Step 1: Proc Bone Armor to 15 stacks, hopefully.
Step 2: Find trash packs or elites and curse with Decrepify.
Step 3: Use Bone Armor as you engage. You want to center yourself in the middle of dense mobs or elite packs.
Step 4: Spam Siphon Blood and at the same time spam Skeletal Mages. This will really have no ill effect on your essence. You can spam as many mages as you spam siphon. I usually just hold down siphon while spamming my mage key. You don't need to "stay" very long because Frailty will take care of the rest. Just make sure you curse often to trigger Decrepify procs.
Rinse and repeat.
I hope you all enjoy!