@Honeybuck
Basically, as far as I can tell when Mu Suyin became the first Soul Tier, he went from 'I have a physical body' to 'I'm a spiritual entity now that can control multiple bodies, which I call Soul Soldiers', along with the same sort of exponential power boost that comes from Tier-ing Up compared to the previous tiers.
This implies that as long as some of his Soul Soldiers are alive, you can't kill him conventionally unless you kill every body at the same time (probably).
His 'original' body seems to have turned into a giant angry mega-cyborg, probably as a result of the close merge with the Dragon Empress, Devourer of Worlds. If you compare how Dragon Empress looks back in Chapter 14 from the glimpse and his more robotic forms, there's a definite resemblance. She also appears to have been some sort of spiritual entity, given she tried to hijack and dissolve Mu Suyin's soul, but failed due to Humanity's most useful trait in this setting being the willingness to give All Powerful Divine Entities the finger, then try to kill them.
Dragon Empress, Devourer of Worlds, had also eaten a number of opponents strong enough to use as Soul Soldiers as well. Those are probably at least some of the bodies that Mu Suyin modified and tended to be seen 'in public' with. He's shown he can make more Soul Soldiers, as well, but useful ones are hard to make. Dragon Queen, as I mentioned, required the legendary Insect Planet's Queen, a massive amount of Divine Metal, and an Earth-Tier Angel's body and/or soul as catalysts, for example.
He's also gotten steadily better at controlling them individually and giving them individual personalities, or letting their body's original personality come back to the fore a bit or something, since when he first used Dragon Queen on Merak, she was mimicking his moves, but later on acts independently of him.
When the Rain Assassin King attacked, he tried to kill Mu Suyin's current body, which didn't work, but appears to have accidentally made him vulnerable in that when he refined a stronger body and the like (twice), it punted him into the Silver Triangle after he killed and ate Rain Assassin King, which led to one of his bodies getting into a fight with Lao Wu.
Lao Wu, being from a Divine Race AND a fallen monk, as well as being ranked as a DIvine General or God's General, is one of the first entities that seems to be an actual threat to Mu Suyin the Spiritual Entity, not Mu Suyin The Current Human Interface Unit. By which I mean Lao Wu can actually kill gods, which is the closest thing to what Mu Suyin is right now.
This led to Mu Suyin needing to try and refine a more powerful body and to hone his powers a bit instead of just brute forcing it like he had been doing so before, as Lao Wu can meet him brute force for brute force once his limiters drop.
Doing so required him to risk his soul merging it with an ancient piece of Divine Race Archeotech, which was the remnants of one of the stupidly-powerful Divine Weaver Race members that were mentioned here and there (You know, the guys some drunken commander from Beiyang decided to open fire on when they demanded Humanity surrender and worship them. Humanity: We're too drunk and belligerent to realize we should lose! Yeah!
).
After he managed to successfully merge, he appears to have possibly hit a level above Soul Tier, or advanced his rank as a Soul Tier, or somesuch.
So Mu Suyin spun off a 'throw away' body to distract Lao Wu, letting it be drawn into Lao Wu's Super Mega God Killer Move, while they finished refining the 'Monster Lady' body for proper combat with him. She also demonstrated that she can use parts of her body as weapons, as she casually used bits of her hair as missiles or kinetic impactors, blowing the crap out of the Qin Fleet and the Dragon Slayer Alliance garrisons. She's also taunting the Dragon Slayer Alliance and Qin family a bit by claiming that she's going to kick the crap out of their prized super-soldier without her own full power.
The crazy (or maybe not, given his theories worked) snake oil salesman with Three Legged Crow is also probably been the first person who isn't Mu Suyin or his closest confidantes to realize what he's doing, comparing his splitting off embodiments to an ancient Chinese Mythological figure who did the same, splitting his soul into multiple bodies.
Hope that helps the confusion and brain overheating!