User blog comment:Circadia/Andromeda, the Disgraced Summoner/@comment-1386905-20121211204725

Her E has two uses, in lane and in team fights. In lane, it's a slightly weirder version of Morgana's Black Shield in that it negates some magic damage and dissuades enemies from attempting to control her (for fear that they will be controlled themselves). As it only works with Magic damage, it's primarily an anti-mage spell (which synergises with her Q's silence to give her a fairly threatening lane phase if played well).

In a team fight, her E is used to try and turn the enemies AoE CC back on them. My thinking is that she would work well with high damage single-target champions like Vayne or Darius who need mobility to reach the right targets. In this case, an AoE CC team like Amumu, Kennen, Nunu and so on shut these champs down because they can longer reach their targets reliably. Andromeda is a perfect counter to that sort of team composition

Imagine Kennen or Amumu pulling their ults when a team fight breaks out. If Andromeda has managed to put her ult down first and pulls her E just before they pull their ults, every enemy in range of her E takes a burst of damage and gets rooted/stunned. The high range of Serenity means it can either be used to dissuade enemies from team fighting in a particular area or, if pullled well, can make it so that an AoE wombo combo team end up killing themselves.