Chuck and Amara's combined energy when they forgave each other created you. Dark and light. You were that. The combination. You weren't one or the other but rather both. Harmony and destruction. You are a powerful creature but you just don't know it because your new to this world.
When you touched down in this earth, you didn't know much but knew everything at the same time. You quite literally did touch down though. In the sense that you fell from who knows where. All you knew is that you crash landed in the forest right will the bunker. You open your senses to the new world to hear Casteil, Sam, and Dean half frantically trying to fight the source of the boom. You had never met them but you knew, just knew who they were.
You: "Sam, Dean, and Cass... I know them. But, how?"
Sam: "Hey guys! There a giant crater here-...." He stops, seeing you