You don't need prediction to use Ice Beam well and it will pay off more than it will cost you. Fpunch doesn't even do that much except hit other rock types which IB will do as well. Plus you should only even try to do anything if you Sub and Gligar comes out. Trying to IB on the switch can lead to beaming something else that comes out and revealing everything but if you Sub first, you don't have to give away Ice Beam.