The Magnet Beam is found in Elecman's Stage. You need to use Gutsman's Super Arm to break some big blocks to reach it, or you can use Elecman's Elec Beam. The Magnet Beam is a step that Mega Man can use to reach places that he normally cannot go to. This is useful in Iceman's Stage and is required to get through a section in the first Stage of Dr. Wily's Fortress.