Kill 50 zombies in one round.
Kill 100 zombies in one round.
Kill 150 zombies in one round.
Kill 500 zombies in one round.
Kill 250 zombies in one round.
Kill 1000 zombies in one round.
Kill 2500 zombies in one round
Kill 10000 zombies in one round.
Kill 5000 zombies in one round.