Starlight and Twilight drink a potion which reveals the downward spiral one of Starlight's alternate universes took. Meanwhile, Twilight watches Starlight take a downward spiral of her own.
A few months prior, Starlight Glimmer drank a potion which showed the tragic demise of one of the worlds she affected when she sabotoged the first Rainboom. Now, she must undo the damage she's caused before it can get any worse.