Yeah, I just realized this is probably getting a little confusing for anyone who doesn't surround themselves with Necrons. ÂÂ
The Obelisk formation has been moved from a core choice to a support choice.  It was a last minute decision on Corey's part and he has seen the error of his ways.
The Monolith (also a support formation) is currently offered as a single unit that you can add stuff to (up to 4 units, Obelisks or Monoliths).  The general consensus is that 3 is the lower limit for the number of units for any formation.  There may be an exception out there but so far, not on this list (war engines excluded, of course).
The discussion from the past came down to 'purists' and 'visionaries' (don't anyone take exception to this, please - it is just an illustration to make describing this easier).  Purists do not like to see units or formations that are non-canon (i.e. don't appear in the 40K realm) so the push was to have the 3xMonolith formation (3M) as the only choice for selecting Monoliths.
Visionaries want to expand the game as much as possible and so have no problems with Obelisks (non-canon units) being attached to such an important formation.  The 1 Monolith + 2 Obelisk (1M2O) formation seemed like the most obvious choice for the basic Monolith formation.
After some lengthy discussion, serious consideration was given to having BOTH formations appear as support formations that feature the Monolith.  Then, in addition to each formation, each one would be able to add additional Monoliths or Obelisks. ÂÂ
I discussed it with Corey who gave it a tentative nod for testing.  In other words, put your money where your mouth is and playtest the suggestion; if it works, it will be modified on the list.
After writing it out, however, it dawned on me the price change between the 200 point 1M2O formation and the 250 point 3M formation was not big enough.  This was not a new revelation and -rewind several months ago- Zombocom and I both discussed that this might not be enough of a difference.  After all, for an additional 50 points you can get 2 more portals which are extremely useful.
Rewind even further and the old pricing for the Monoliths was 75 points and the Obelisks were 50 points.  While the Obelisks were priced fairly, most would agree that the Monoliths were underpriced at the time.  So Corey and I created a pricing structure that you see in
Raiders that discouraged single Monolith play (125 point Monolith) but still allowed it.  But the popcorn concerns continued, this time with 1M1O formations dominating the issue.
Fast forward back to present day.  The goal now is to create a 3-5 unit formation that is built out of Monoliths and Obelisks.  That might be a 1M2O formation, 3M formation, or 3M2O, 1M4O, or whatever floats your boat.
The difference in opinion isn't about the formation itself but how to represent it on the army list.  The two separate formation idea would certainly work.  I just think it looks horrible and it can be simplified.  To paraphrase E&C: if something can be made simpler it should be.   I would agree in this case and suggested the formation to be written out as...
1 Monolith plus 2-4 Obelisks or Monoliths.It allows for everything everyone wanted and is very simple to write out and understand.  So that is the lengthy description and hoepfully prevents you or anyone else from having to comb through the 9 pages before this.
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author of Syncing Forward and other stories...It's a dog-eat-dog world, and I've got my Milkbone underwear on.