I used the princess sister chick.
Her freeze attack is easier to use in this level because it has little homing bits o' ice. The thing is, you really need to do it in one take because if you don't do the last part without a full tank of magic, you'll get stuck halfway through.
The strategy is to shoot off your ice attack (at the part near the end where you have the big jumps), and try to jump on as many frozen enemies as possible to the next perch. You can maybe cross over 2 or 3 perches in one shot someitmes. It's tricky because sometimes dudes will be frozen right over your perch and you're going to die when they wake up.
The boss is easy in retrospect. The green guys won't jump at you if you are right on top of them. And you can otherwise slide through the knights. So I just slid through the enemies, got on the rising platform, made sure I was on top of the green dudes so they don't jump out. Then hop on the other platform and wack the bell a bunch of times. Rinse, wash, repeat. You need to get it to ring 3 times.