3-Player Push META

Trash Killer
Nova Necro, Natalya DH, Meteor Wiz, Scythe Necro

This position usually requires a build with good Area of Effect (AoE) damage like Death Nova or Meteor and huge temporary buffs like Arcane Attunement, Spellsteal, Assimilation etc. The main task is executing the damage rotation properly in order to progress through the Rift. With a double-support setup, the build must also be powerful enough to finish off the Rift Guardian by equipping Bane of the Stricken.

Main Support
zBarb, zDH, zMonk

The main Support role requires good pull abilities, good overall damage & toughness boost. The main task here is to pull monsters together (for Area Damage value) for the Trash Killer, drag Elite packs along, scout the map and keep up damage & toughness buffs.

Secondary Support
zDH, zMonk, zNec

The second Support usually provides even more toughness and damage buffs to the group. The main task here is often very simple: Keep up all buffs while sticking close to the damage dealer. Sometimes the second Support also helps to scout the map and engage enemies.

or Rift Guardian Killer
Rathma Necro, Spider WD, Impale DH, Invoker Sader

The RGK requires a build that revolves around high single-target damage, often combined with fast attack speed skills to stack Bane of the Stricken.

Concept
With two supports, this plays very similar to a 4-player group with the exception that the boss kill is slower, so you should use a build that can both clear the rift well and finish off the RG. In Season 34 there's several conteners for this role of all-around DPS: Raiment Generator Monk, LoD Death Nova Necro, LoD Wave of Light Monk all have a legitimate shot at it.

Raiment Monk is the Strogest DPS of season 34, with their only major problem being survivability. Luckily, with 2 supports that becomes a lot less of an issue, and at high enough Paragon you can even kill the Boss without Bane of the Stricken giving you space to run a defensive gem.

Death Nova Necromancer exels at decimating large packs of monsters thanks to density scaling of Bloodtide Blade. Simply wait for all the buffs and CC to be set up and spam some Death Nova into it. This uncomplicated strategy is nearly guaranteed to blow any enemy to smithereens. This build however, perform terribly against the Rift Guardian so you have to save some pylons to create density with Nemesis Bracers.

Monk with Sanctified Wave of Light has slightly less AoE damage but fares much better against bosses and is virtually invincible.

The Trash Killers are supported by a zBarb pulling Elites and grouping monsters together with Sanctified Whirlwind. On top of that, the Barb provides massive toughness buffs with Ignore Pain Mob Rule and War Cry. Additional offensive and defensive buffs are provided by the zDH.