Against all the walkers they already got value against you so it's an answer but maybe not a specifically great one. Counterflux is a true "answer" against a lot of those cards, this is more of a response.
Mentor this may not even kill depending on what sorta state your opponents hand and mana situation is in, not to mention the tokens.
I looks like the answer that PO might need to come back. It also is the mirror breaker.
It definitely doesn't look like a mirror breaker to me. One for one'ing against planeswalkers doesn't work well, as your opponent has already grotten value out of their planeswalker. It's a card worth considering, though.