The name of this game is farm exp, gear, and gem upgrades as quickly as possible by running GRifts as high as we can as fast as we can. This is not for pushing solo leaderboards, nor for group speed runs. To do this quickly and easily, we intend to maximize our Mystic Ally's (MA's) damage as much as possible by buffing their damage and attack speed and debuffing mobs' damage taken and movement speed.
One thing to watch out for: your MAs will not always stay with you. If you run far enough away, they will teleport to you eventually, but if you Dashing Strike through one group of enemies and start meleeing a second group of enemies at the point you dashed to, your MAs are likely to stay on the first group and if you're in a position such that your Cyclone Strike doesn't affect the first group (you dashed into a second room or through an elite Waller's set of walls, or whatever), then your MAs won't benefit from the 200% damage boost to those mobs and those mobs won't have 30% damage taken debuff from your Inner Sanctuary. The end result is your MAs will take longer to clear that first group while you're stuck soloing the second group and your overall dps will suffer and time to clear the GRift will increase.
My general strategy with this build is to use Dashing Strike primarily for movement and run when it's not available. I use Cyclone Strike on every mob I encounter and let my MAs quickly destroy the smaller packs (1-10 mobs) while I keep moving to the next group and let my MAs run/tele to me. For larger groups and elites, I will stop momentarily to debuff everything and get the Pain Enhancer stacked up, and the resulting explosion is very satisfying. If I dashed into an elite and it's not dead before the AS buff wears off (4 seconds), then I will Dashing Strike in place to pop the AS buff again for another 4 seconds to finish it off. This usually only happens when the elite or elite pack is in a large group of mobs so my MAs are distributing their damage all over the place, which means I'm spamming Cyclone Strike and everything is dying faster from the Dashing Strike AS buff anyway.
Keep in mind any buff applied to you and any debuff applied to mobs has its effects scaled by a full order of magnitude because of your 10 MAs (plus your follower to a lesser extent).
Always be on the lookout for Nephalem Glory Globes, and after finding your first one be sure to pick up every Health Globe afterwards without backtracking too much (i.e., don't waste time going out of your way to grab 1 Health Globe, but a side-step on your way to the next group of mobs would be considered necessary). With the GRift run times at less than 5 minutes and the speed with which you're destroying packs of mobs, you should easily be able to chain one Nephalem Glory Globe all the way to the end of the GRift.
For this build, I like bringing my Enchantress for the always-on 3% AS buff (Level 30 Skill: Focused Mind). Secondarily, her level 25 skill Erosion on a 15-second CD to debuff enemies with an additional 3% damage taken is handy when it lines up on an Elite or RG. Thirdly, her Level 15 skill Charm will very rarely charm an elite mob to fight for you, which can be nice.
This is my first build I've published here and it's mostly for my own notes, but since I hadn't seen one like it yet I thought maybe others could find some benefit. Any questions, comments, or thoughts for improvement would be greatly appreciated! With this being my first guide here, it's highly likely I've overlooked something and I believe healthy, constructive debate has a lot of potential for improving processes.