if we go with her being the real final boss we should give her strong superpowers that have a connection to who she used to be
Angels in religious stories bring happiness and blessings, she could instead bring torment and death, but a slow death, like every living being she touches/is close to slowly rots and withers away in agonizing pain (dovegirl should be resistant to this, but not immune), some other extra powers are needed to give her more than just a passive effect, maybe the rays of corrupted lights i wrote about in that other thread, or just superhuman strength ig
(i have this cinematic shot in my head where she slowly and expressionlessly walks towards a cowering man, his flesh slowly begins to wrinkle and grow tumors as he begs for mercy, ultimately she gets within reach and gently caresses his cheek which causes the man's eyes to leak blood and his organs to be liquified and vomited out, but him being unable to vocalize the agony he is feeling)
Her being a blob inside a doll means no wings so the thing about her floating/flying in the sky can be left out

Her final move could be a suicidal one: she unzips her chest allowing her full power and hate to pour out of the vessel, shattering it and engulfing the whole world (or part of it idk) in a curse or something along those lines
also just to give her an additional reason to be evil her vessel could be imperfect or otherwise unable to properly contain her full power (this could be why anyone standing close to her starts decaying, or, even better, the more dovegirl fights her the more her vessel is damaged and, therefore, the more corruption seeps out of her) which translates to her "living" on borrowed time: as her corruption grows she is destined to die sooner or later so she wants to bring ruin to as many people as possible as fast as possible

As to why holyfield would team up with a creature that only desires pain and suffering (if such a thing could even be possible) we can think of something im sure, maybe he managed to contain her and was using her corruption to water the lolis he grows?