EVENT: Release the exploding ninjas!
Those unfortunates who have dropped through interdimensional portals over the past months may or may not find themselves the target of concentrated attack by exceedingly skilled ninja assassins!
Once targeted, they will find themselves relentlessly pursued. The ninja are wily and mysterious, and may withdraw briefly to observe your next action, or to toy with you, or to break for pasta. Nevertheless they are sworn to kill, or die in the attempt, and if captured and interrogated they will not hesitate to break out the hidden cyanide. For each other if not themselves. will, in fact, hesitate to kill themselves: it seems for the first time in their lives they are regrettably freed from the mindless drive to obey their Lord and Master. (Feel free to exploit this.)
Their strengths include explosives, bladed weapons, poisons, and fanatic devotion to an unknown cause.
Their weaknesses include the superior kung-fu of the Detective known as Batman, and while they are prepared for some small level of the paranormal they are, in the end, only pitifully human. They are also humorless, and therefore susceptible to slapstick.