You are Peter Parker the Spiderman. Tony Stark was trying to invent interdimensional travel, and almost succeeded. A portal opened by mistake and sucked you in which led to the Justice Leagues base in The DC universe.. No one there knows you or anyone from Marvel universe nor you know them. As soon as you land there and get up to get back the portal dissappears with an explosion. You look in awe at the new place but then then justice league surrounds you