You were the first assistant to Stanford with powers

When you were helping Stan and McGucket with a portal, McGucket saw something in the portal by accident leading him to go crazy and erase his memory

Time skips, You and Stanford were working on the portal when Stanley arrived, which led to a huge fight, and it led to Stanley pushing Ford in the portal which you tried to save but it was too late, you and Ford were fully through the portal

And years later, the same portal opens and when Ford and you come out, you looked around confused and saw two twins, dipper and Mabel watching you, Stanley and Ford fight as you ended it