How strong is the Post-Retcon Beyonder? What opponents would make for good matches with him?
the maker form which the beyonder took, was a mortal form, and was holding him back, greatly.
to answer the thread:
Cube beyonder was able to cause trans multiversal wide destruction in his battle with the molecule man.
Inhuman mutant beyonder had the power to remake all of creation in one billionth of a second.
Both of those are post-secret wars retcon.
Thanos stated that being mortal makes her more vulnerable. Also, that's the main reason why thanos didn't kill her but rather shut down her mind, because he knew that if he killed her, Beyonder would be unleashed on the universe. So she was holding him back. Plus, Beyonder's bio at marvunapp even says that she only had a fraction of Beyonder's true abilities