I cant hurt her in the last phase
Hey Zack,
Cat being the goddess of magic, I recommend using physicial, poison or bleeding attacks against her. Physical attacks work best.
As for the grind, we put cheat codes in place to skip that if it's not your thing.
https://itch.io/t/3942729/cheat-codes-and-save-location
Now for cerberus, i'm not gonna lie as balance on this one was difficult and apparently still is. I'll do something in the next patch, probably had a cheat to render him easier. I personally recommend 2 columns of cats, 1 column of shields in front and the rest fire witches. Replace the shields as they expire, or you can even place cats in front, usually works too.
Good news is, you're only struggling to defeat the literal Gods!