When you pause while your dead in any Forest Map (exception of Forest I and II), and wait till everyone kills the titans, you'll see that your character is still dead even though you should have respawned at the last titan kill. So i tested it and made it lure a buncha titans and purposely let them, smash the clone (didn't work), grab the clone (didn't work also yet it is stuck at an infinite loop of grab and bite animation) , flop (didn't work also) ,side bites and frontal bite (not yet tested atm i'll try later).
TL:DR people
Basically if you pause while dead and someone kills the last titan, you get an unkillable clone when you unpause.