Oliver is in Training with Mare Barrow when she is under the identity of Mareena Titanos. She sees him create a miniature whirlwind between his hands.
He becomes a member of the Shadow Legion. It's the legion that Cal leads after he thinks of it. The Shadow Legion will be the first completely Silver legion going into the trenches. They will appear to be Reds, but when the Lakelanders attack, they will be able to use their abilities to fight back.