Lots and lots of adorable and cute Rippers , wiggling around. Because hell I always had plenty in my armies. Double cuteness bonus if they have wings.
If you are chaos, call forth a daemon lord (world WILL end at that point). Orks and eldar would run and live to fight another day. Imperium would do about the same except declare an exterminatus on the entire planet.
regarding zoanthropes. They are easy to wound but they have that annoying 3+ invulnerable you have to chew through. Otherwise just as vulnerable as a tyranid warrior to a missle/ lasscannon.
