Some of you may already know this, but it took me a bit of time to learn. When playing as Iorek, if you press and hold down the A button, you'll strike once and then blue bubbles will flow into Iorek. Once you let go of the A button, Iorek will do a superstrong attack. This is easiest to do after tackling someone/something (running and pressing A at the same time). All you do is tackle, but don't let go of the A button after you finish tackling and you'll do a power attack as soon as you let it go.