Board Thread:DC's Legends of Tomorrow discussions/@comment-807326-20170201024559/@comment-25811707-20170201160351

So Black Flash comes because of the nonexistence would catch up to Thawne so Thawne needs the legion of doom, and if he stays in one place for too long then black flash comes. Which is why he always leaves in the middle of a fight or a meeting with his teammates. He must have a timer set for if he stays in one place the Black Flash appears. Basically, if Thawne stays in one place too long the Black Flash will come for him.