any advice? pet is tier 12, just tried once & was easily defeated

A good dark blocker, a magma/fire/ice blocker, a surplus of freezing scrolls, and some luck :)

for future reference, the real secret to winning is to try more than once. This careaper drops the Lucky Scroll, and there's definitely a reason for that. He definitely takes a significant amount of luck to beat, even on the first win. I found cronus blade and ME to be very useful against him.