From the Super Mario Wiki
Monstrous Magnets are enemies in Wario World and resemble large, flying green magnets with one red "N" end and one blue "S" end.
They appear in Beanstalk Way, the second stage of Thrillsville. They try to attack Wario by firing electrical blasts of energy at him. Wario can use them to get to higher places by throwing them headfirst onto metal boards, which they stick to for a short time.