Board Thread:Theories and Speculation/@comment-36512555-20191115151404/@comment-4912646-20191115162802

I agree that the whole sequence with Madara's Susanoo is weird, but we don't really have a lot to go off of here. At the time these chapters were released, the wiki (and fanbase at large) actually did assume these new Susanoo forms were meant to be two different versions of the same thing ( a "stabilised" form and an "unstabilised" form). But then as time went on and other users started using the stabilised form without showing an unstabilised form, everyone started assuming that the big cloaked form was actually just Madara's third stage ("armoured") form and the samurai-esque form was an entirely new fourth stage. This is backed up by the databook, which only shows the stabilised version in its "Complete Form Susanoo" entry, though it has other issues like only listing Madara as a user.

It's worth noting that in the next chapter, right after Madara announces he'll use his Complete Form Susanoo, Mei asks if "that" (the unstabilised cloaked version) is the "true Susanoo", and Madara tells her "not yet" before stabilising it. So this could be interpreted as Madara merely saying he's about to use his "Complete Form Susanoo", but not actually doing so until the next chapter.

Of course, none of this explains why Madara's third form is so different from other users, especially with its colossal size. But then again, later on we see Sasuke increase the second form's size to rival Kurama, so it's possible Madara was just choosing to make it that big both times he used it.