I think the way it "technically" plays out, is that the IC holds the characteristic for the MC. Remember, the IC storyform is how it affects the MC, not how it affects the IC.
Lego 2 had this.
Here is what I see.
The IC holds the alternate view of the MC, trying to push him to stop/reconsider/etc. It's going to look different for Start/Stop character, and Success/Failure plot. But the IC can represent his alter-ego. Or the RS character can be the alter-ego.
But, when the MC gives in to what is not good for the story goal or for his personal goal, he is his own antagonist. His DESIRE for the thing the OTHER is holding out is where he's chewing his own foot off, so to speak.
The OTHER can be neutral as far as the story goal. The IC is not necessarily involved in the actual OS. But the antagonist is. So the antagonist can be the MC.
As I've worked through the Dramatica options for this, I found this...
- When the MC and the RS share the same problem, the outcome is failure.
- When the IC and the OS share the same problem, the MC is steadfast.
- When the IC and RS share the same problem, the OS is the same problem, the MC is steadfast, and the outcome is failure
- When the OS, MC, and RS share the same problem, MC is change and outcome is failure
In any of these combinations, you could have his self as his antagonist. In one case you have the RS with an alter-ego (didn't they do this in a way with the IC in Split?) or a future self (as in Lego 2). In another case you can have the real desire he's fighting against personified by the IC.
If the MC is his own worst enemy, the RS can be with himself, or with a devil's advocate of himself, like in Lego 2. (I feel like I'm walking on thin ice here, please correct me if I'm misunderstanding RS, @jhull, I did not go through all the RS lessons covered last year).
Who is the antagonist in A Christmas Carol?
Just my take. Besides, if we can imagine it, it can be done with Dramatica.