User blog comment:JmLyan/Magnus, the Attractive/@comment-4652200-20140618163154/@comment-7481207-20140618190953

It is meant as a punishing effect for incorrectly using spells, although maybe too punishing. It was mostly meant to punish using E without first making sure only enemies will be hit by it, and the rest of the kit just kinda also got that effect to make it be "hit ally => stun".