Incumbent first-five Beauden Barrett delivered the most astonishing performance in the All Blacks' last test to prove he is the country's best play-maker and automatic choice to start at No 10 if he's fit.
But the selectors need some answers about what they might do in future should Barrett be injured or in need of a rest.
If Mo'unga can prove in Nelson that he can handle the demands of the starting role, it may be that he effectively jumps to number two in the pecking order, but only in the sense that he would start ahead of McKenzie — not oust him from the regular match day 23.
McKenzie's pace and versatility have been lethal weapons off the bench this year and the All Blacks want to keep that in their match day mix, especially as the 23-year-old can slot in just as well at fullback.
The return of Milner-Skudder was just as heavily signalled by the selectors but no less significant for it. The Hurricanes wing, like Mo'unga, was long pencilled in to start this game. Ideally, the coaches wanted to have a look at him in June against France but felt he lacked enough game time to make the right sort of impact.
There's a strong symmetry with last year for Milner-Skudder as he returned to the All Blacks fold in the corresponding fixture in much the same circumstances.
He only recovered from a broken foot to play in the last few weeks of Super Rugby in 2017 and it took him until early September to rediscover his sharpness.
He has been released to play for Manawatu in the last few weeks to find that last edge the selectors thought he needed after again missing most of this year's Super Rugby competition after recovering from shoulder surgery.
They think he's ready now to once again remind the world that he has an astonishing ability to beat defenders with his pace and footwork and give the All Blacks a different sort of option to the power game offered by Rieko Ioane and Waisake Naholo.
All Blacks head coach Steve Hansen said: "While we've made a number of changes from our last outing, this is not a reflection on Argentina but rather a desire by us to grow the experience and depth of our squad.
"Secondary to that, we also know that if we don't use the whole squad across a long season, we'll run out of steam later in the year."
Frizell wins a second start at blindside after impressing in his first and that change is considerably more about seeing what he can do than it is about giving incumbent Liam Squire a rest.
All Blacks
v Pumas, Saturday, 7.35pm
Trafalgar Park, Nelson
15. Ben Smith
14. Nehe Milner-Skudder
13. Jack Goodhue
12. Ngani Laumape
11. Waisake Naholo
10. Richie Mo'unga
9. TJ Perenara
8. Kieran Read
7. Ardie Savea
6. Shannon Frizell
5. Scott Barrett
4. Brodie Retallick
3. Owen Franks
2. Codie Taylor
1. Karl Tu'inukuafe
Reserves: Nathan Harris, Tim Perry, Ofa Tuungafasi, Sam Whitelock, Luke Whitelock, Te Toiroa Tahuriorangi , Damian McKenzie, Anton Lienert-Brown