I mean Composite Servant is already MFTL+ and 4-B, Combined doesn't really make a difference at that point.
He'd have conceptual death hax (King Hassan), Mystic Eyes of Death Perception (Shiki), soul hax with a glare (Goetia), Type 5 via lacking a concept of death (Tiamat), Immeasurable speed (Edmond Dantes), and a whole bunch of other shit.
Just things like Garmadon dying, being revived and becoming evil again, anything involving the Onis and Dragons, there being a multiverse, just a bunch of stuff I never saw in the show because I dropped it back then, and now they've introduced so much stuff.
Long story short, Wu becomes a adult, finds a super armor that used to be his fathers, gained the respect of the mother of all dragons, and distracted Garmadon long enough to melt him with her fire. Then he turns to smoke and reforms, claims to be unstoppable and says that he is fueled by their conflict and one-shots here.