This has undoubtedly been done many times, but I haven't seen it in AT and it seems powerful to the point of absurdity so I guess I'll throw my build out there. This is a little long-winded, so just read the paragraph or two after the actual builds to get the synopsis if thats all you really want.
4x:
Soul Reaping: 8
Blood Magic: 4
Curses: 9 + 3
Death Magic: 12 + 4
Animate Bone Fiend
Blood of the Master
Taste of Death
Rend Enchantments
Mark of Pain
Barbs
Blood is Power
Vengeance
4x:
Divine Favor: 12 + 4
Healing Prayers: 12 + 1
Divine Boon
Orison of Healing
Healing Seed
Heal Area/Light of Dwayna/Healing Breeze/Infuse Health (1 on each)
Arcane Mimicry
Arcane Echo
Vengeance
Unyielding Aura
Before the battle starts, the monks kill themselves with BiP (which they mimicry'd off the necros), at which point bone fiends are summoned, and then Vengeance comes down on the monks. This is repeated with Vengeance, Echoed Vengeance, Unyielding Aura, and then finally with the Necromancer's Vengeances. Each Necromancer has Soul Reaping 8, so they have just enough mana to keep it going. The actual order of casting these spells is fairly complex (the most efficient solution I have found follows no regular pattern) but in matches where there is a prolonged period before the first confrontation there will be an absurd number of bone fiends on your side of the table (if you consider that you get 1 bone fiend per death, or alternatively 1 bone fiend per raise since you all start off alive and end up alive, you get 8 Vengeances + 4 Unyeilding Aura + 4 Arcane Echo + 7 Light of Dwayna = 23 bone fiends--this should happen in well under a minute if done well, and after this most abilities should be recharges so it can be repeated if a confrontation is avoidable, as frequently in g v g). During this process, the monks may cast Heal Area to heal the bone fiends (and necros) and the necros use Blood of the Master.
Obviously this will work out differently depending on the format, but in most formats (certainly those with periodic rezs or NPC defenders) from my experience the opponent will not be extremely eager to engage on your starting location (and letting the opp get 1 morale bonus is nigh on irellevant in g v g, since you will have 37 fiends instead of 22). At this point, you may have to move to fight the enemy, or you may be able to simply sit back and mass 15 (you will probably want to cast Light of Dwayna only once, since otherwise the dp can potentially cause serious issues--this is obviously not the cast in annhilation games, but I assume you won't be able to sit around in annhilation games either) more fiends each minute until they decide to make their move.
Once you move to confront the opponent, you will have access to Barb and Mark of Pain--both exceptionally powerful here. Rend Enchantments on one target, throw on Barb (if they have clustered targets take one and put on Mark of Pain) and focus. Though the opponent may remove the hex quickly, it is unlikely that you will not get in 1 volley. Given that there are at least 20 attackers, the added damage from Barb alone should be around 200--in addition to the actual damage. Ow. If they were foolish enough to leave 2 warriors together or similiar, Mark of Pain will be hitting for well over 600 shadow damage in a shorter interval than most healing's cast time. In any case, there is pretty much no one who is still alive after that volley, and anyone standing next to them is badly hurt if alive. You have 3 more necromancers, so just switch targets and repeat.
If the opponent uses serious aoe (though fortunately most people don't pack hate for this kind of mob in pvp), they should be triggering a load of Healing Seeds (effectively negating something dumb like Maelstorm or Chaos Storm). Otherwise, unless the blow kills all of your fiends within 1 second (unfortunately a possilibity) as many necromancers as are necessary may respond with Blood of the Master. The necromancers all have access to practically instant 200 point self-heals, and so keeping up BiP on the monks is laughably easy. In general, with consistent doses of Master's Blood it seems unlikely that the opposition will be able to stand up for long to focus fire from 24 fiends.
If you do have multiple opponents packing serious aoe (or mark of pain) which can take out a significant portion of your fiends before you can respond, keep in mind that even 10 fiends is a lot, and just try and keep enchantments off their monks and take them down. When someone tries to rez, just do your best to get the kill first (if they are rezzing and not protecting themselves there is a good chance that 2 volleys from 10 bone fiends and your whole party will finish them).
If your opps pull out Edge of Extinction, you can actually adapt and play as though you were a very inefficient edge of extinction + mass suicide build. Due to the fact that they will have to leave you alone long enough to kill a couple fiends, this might be able to barely work, but it requires much coordination and is generally not desirable.
J
Perhaps I need to spend more time working on an answer to edge of extinction, since it can really give me problems.