Lady Kronika, the primary antagonist of MK11, is at full power here with her spoilers:end of spoilers to set up shop in:
fully powered up crown via Shang Tsung's Well of Souls and her Hourglass
Round I) Composite DC Universe.
Round II) Composite Marvel Universe.
Just how dangerous could she be in these universes?
I would give her Geras and Cetrion, but as of the final chapter of the MK11 Story Mode (I have seen leaks of the entire Story Mode being posted on YouTube early; I downloaded them before they were yanked), spoilers:end of spoilers
Geras is out of play due to being cast into the Sea of Blood, which is, according to Raiden, "completely bottomless"--and since Geras can literally revive himself from the dead, he literally can't do ANYTHING to bring himself back because he can not die by drowning. Regarding Cetrion, after being beaten by Fire God Liu Kang (due to Raiden binding himself to Past Liu Kang's soul after Revenant/Dark Emperor Liu Kang absorbed enough of Past's soul), she sacrificed herself to power up her mother (Lady Kronika), something Cetrion herself reveals earlier in the story.
As for Lady Kronika, at full power (and with the Sands of Time hourglass), she was able to spoilers:end of spoilers
rewind time completely, as the combined armies of Outworld (under Kitana Kahn, after Kotal Kahn passed the Kahnum to Kitana due to being crippled by Shao Kahn), the Shokan under Queen Sheeva, the Cyber Lin Kuei(?) and the U.S. Special Forces were about to invade her keep. Their invasion was literally reversed when she manipulated time to that extent (kind of like rewinding an old VHS tape), similar to Whis' ability to rewind time up to 3 minutes into the past.
Don't get me wrong; I am not trying to hype up Lady Kronika. After all, she still spoilers:end of spoilers
required some of Earthrealm's Jinsei for her plan to rewrite history. Not to mention that the game makes it unclear if her crown needs to be in constant exposure to the Well of Souls, or if her crown had absorbed enough soul energy for her plan. However, Classic Jax wore this crown and managed to take down Cetrion for the first time.