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. Masquerade Bone Spear fits the bill perfectly and doesn't really have any competition in this slot.

Bone Spear Necros prefer to stay far away from enemies and blast them with Bone Spear while getting a massive damage bonus from Blighted Marrow if many enemies are grouped together. This of course doesn't work quite as well against the Rift Guardian but it's not a problem Bane of the Stricken can't fix.

The Trash Killers are supported by a zBarb pulling Elites and grouping monsters together with Ground Stomp Wrenching Smash. 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.

Concept
Similar to the above setup, a support Barbarian (or Demon Hunter) pulls enemies together for massive Area Damage value but we drop other valuable buffs from the missing support. This is generally harder to play but necessary for builds that have low boss damage such as Death Nova and Grim Scythe.

Technically this setup can be played with any combination of the top tier Trash Killer and Boss Killer builds, but the top choices in Season 31 are always gonna be Necromancers.

Both Bone Spear and LoD Death Nova are top picks for the trash killer role. The former can now focus solely on AoE damage while the latter actually becomes playable with an RGK on the team. Overall Bone Spear is the stronger build between the two but Death Nova has larger AoE and is easier to play.

As far as supports go you actually have a choice to make. The default option is keeping the zBarb who gives you much better grouping and defensive bonuses but little in terms of damage buffs. In comparison zDH provides a lot more damage but less defense and they need to use Natalya's Vengeance setup to do pixel pulls which can do the job fairly well but can be very difficult to execute depending on the mobtype. And, of course, without Rage Flip your pulls are never gonna be as big.