Family stick together
Since the fight had started, Galen had been staying in Minny's shadow space. It was an order from their mother, Layla. On top of that, Layla stated that if Minny ever felt like she was in danger, then the two of them would just have to stay in their shadow space until they thought it was all over.
These were the two conditions that had been set out by their mother in order to allow Minny into battle, but there was one problem. This all relied on Galen actually listening. Somehow, Galen also knew how to use the power of the shadows.
Whether he was secretly taught it or just learned it from observing the others, he knew the shadow powers. This meant he was able to escape from the shadow whenever he wanted to, and that's what just happened now.
'You stupid brother!' Minny thought, staring at him. 'Why aren't you listening to Mum's orders? She's going to kill me if she finds out about this.'