If a witch were to appear in front of you in a puff of smoke, you'd probably be transfixed — you'd be standing there with your mouth open, unable to look away, as if held by some magic power.
You'll notice the word fix in the middle of transfixed. This kind of fix means "fasten," as when you fix your eyes on the clock, or you affix a stamp to a letter. When you're transfixed by something, you’re fastened to it. Scary things can transfix, but so can beauty. When you go to the top of the Eiffel Tower, you're likely to be transfixed by the view of Paris and never want to leave.