https://www.icy-veins.com/d3/follower-skills-and-gearing-guide

https://www.icy-veins.com/d3/templar-follower-skills-and-gearing-guide

The recommended abilities for the Scoundrel are:
Level 5: It is important to note that hard crowd control from skills is something your build might want to avoid — either because it prefers to control the fights itself and CC might hamper that, or simply from speed farming considerations. In such a case, do NOT select a first skill, as there is no way to unlearn it and you will have to re-level a new character simply to get a “fresh” Scoundrel to accompany you. Otherwise, we recommend Powered Shot — a hard crowd control ability that can save your life and offer you a moment of respite every 8 seconds, topped off with a Dexterity-scaling duration.
Level 10: Anatomy — a passive buff to Critical Hit Chance that scales with Dexterity on your follower equipment.
Level 15: Piercing Shot — a boilerplate 10% damage buff against enemies affected by this skill; once again, its piercing properties lend themselves well to character builds that displace enemies into clumps.
Level 20: Night's Veil — the highlight of the Scoundrel abilities, this circular AoE effect covers a decent 20 yard area and guarantees critical hits against enemies caught inside. Needless to say, this is a massive damage boon whose duration scales with Dexterity, and is the prime reason to take the Scoundrel.

Scoundrel Setup - Solo GR Pushing
The following setup reflects the best-in-slot item choices and gear rolls for a Scoundrel taken to Greater Rifts with the intent of pushing leaderboard. Note that you can either focus on Crowd Control with the inclusion of Blind Faith, Cord of the Sherma and Cluckeye in the setup, or do a straightforward “buffing” Scoundrel with Leoric's Crown, String of Ears, and a generic bow or crossbow. Tal Rasha's Relentless Pursuit is included due to its innate Increased Attack Speed roll, but is not a necessary part of the setup.