So, what do you think Valentina would change? (Spoilers)
Valentina likely has a perfect memory, so her version in the new timeline probably has a very good idea of what is going to happen.
Heavy mentions that he was weak, at first, and could only do parlour tricks - that most superpowers actually began like that.
So Valentina likely knew when Heavy would appear, and thus when to hit him - be it through Etienne's influence or just literally hitting him - so he never becomes a superpower.
Magus is just a guy who knows a lot, but nearly powerless without the Pyramid - Valentina and Etienne could easilly prevent him from ever rising to power.
Without Magus, no Eliza selling her soul to Hell*
And Masumi... She would be the trickiest of them. But Valentina knows how old she was, even assuming Valentina didn't know her family or her exact date of birth - once Etienne knows what's at stake, he could likely prevent everyone in Japan from having sex for some years, in order to avoid Masumi's conception.
We would have a world without any superpower other than Valentina and Etienne.
Only three issues:
* Without Magus gatekeeping magic, people could find it by accident, and chaos would issue
* Eliza is/was/will be still burning in Hell. If she finds a way to influence the world...
* The Queen. Without anyone to help her, Valentina would not be able to stop the Queen.
(IMO, the Queen is Valentina after a few thousand failed loops - same power level, same kind of "polarity", trying to do good)
And about you? What do you think Valentina would try to do differently in the second loop?