When they first visit Shang Tsung's Lab in Season 3 of Invasions Mode, Mortal Kombat 1 players won't be able to find a single Klue. However, after they've beaten Arctic Sub-Zero and gotten their hands on the Cryomancer Heart, they'll be able to return to the mesa and open up the icy gate on the second floor; through which they'll find the REWOP RATS Klue.