Quoted from bobukcat:(...) Without a doubt the hardest one is to complete Rescue Multiball, I've been close once and that's it. It is like a final wizard mode unto itself it's so difficult.
I get to the halfway point about 25% of the time (Ding Dong The Wicked Witch is Dead), so I can say that Rescue MB is the toughest of the 4 starting crystals, but not too hard if you learn to trap the ball on the castle upper PF and shoot the 'search' loop. If your timing isn't great, it also helps to try to get the ball to the upper PF during any multiball modes and just smack away. Get a few letters each time and you'll have it soon enough. Another trick is to trap the ball, let it roll to the tip and hit that flipper once and then trap again. Usually the ball makes a more sideways trajectory that will ricochet a few times and get a couple letters before trapping once again.