ATTENTION: This guide is actually an amalgamation of two guides on the old Bioware Social Network (BSN) forums, one guide by known_hero and another guide by Antmarch456. Known_hero wrote his guide in December 2012 and Antmarch456 wrote his guide in September 2014. They are very similar so I am combining them into one guide.
First let me say that I take zero credit for this idea. All credit goes to it's creator: Scrogublitzen. This build was
originally for ME2 but I will translate it to ME3.
An invisible sniper biotic, how awesome is that!!! Seriously, this is one of the best builds I've ever seen. I never got a chance to try it out because I've been playing a lot of ME3 lately. SOoOoOo, I decided to see try this out in ME3. I just started out but this is already the most fun I've ever had with this game.
Scrogublitzen's The Reaver is a sniping Reave Infiltrator. This build's original intention was to strip enemy protection while keeping the Infiltrator alive when sniping. The ME3 version still keeps this strategy alive but with Reave's biotic explosion capabilities, this build is even more dangerous.
Powers:
Tactical Cloak: Damage, Recharge, Sniper Damage
If you want to stay cloaked after using Reave (so you can use Reave twice), take Bonus Power at rank 6 instead of Sniper Damage.
Sticky Grenade: Damage, Max Grenades, Damage
Reave: Radius, Damage Reduction, Damage and Duration
You want Reave to work as your protector and a biotic weapon.
Disruptor Ammo (squad version): Squad, Headshot, Stun
-OR-
Disruptor Ammo (Shepard-only version): Damage, Headshot, Damage
known-hero used a squad version. Antmarch456 used the damage version.
Cryo Ammo (squad version): Squad, Headshot, Damage Combo
-OR-
Cryo Ammo (Shepard-only version): Duration, Headshot, Damage combo
Only known_hero used cryo ammo in his build, and he had both Disruptor and Cryo on squad versions. ScroguBlitzen's original idea was for the squad to have Disruptor and Shepard use Cryo.
Operational Mastery (6) - Weapon Damage, Weight Capacity, Damage & Duration/Sniper Rifle Damage
Rank 6 depends on preference.
Fitness (6) - Durability, Shield Recharge, Durability
Weapons:
This build was originally intended for snipers so use your favorite SR. I suggest using a pistol or SMG for those non sniping situations. Something really light like the predator.
Squad mates:
Both known_hero and Antmarch456 suggested Liara for priming/detonating and crowd control.
For the 2nd squadmate:
- known_hero suggested the second squadmate should be used to stagger enemies for sniping.
- Antmarch456 suggested the second squadmate should be able to wipe Barriers/Shields and armour; he stated that Garrus, EDI or Kaiden are good choices.