Zombie Army 4 Dead War - A sneek peek at waves 12 thru 21

I looked at what achievements I had left in Zombie Army 4 - dead War and one of them is, going 20 consecutive waves on any Horde Mode map. The easiest way to achieve the achievement is to get a few buddies together. Set the game up on EASY, and one players' worth of enemies. make sure you do not believe this will be an easy fight. It gets a little bit harder on each wave. have a look at this video to get an idea what is going to come, and how much of it - on easy and one player worth of zombies. There were several waves that were too close for comfort, and the Rejuvenation perk saved my buns several times - I highly recommend utilizing that perk !
ZA4 /Rebellion considers the wave counted when you complete it, and the next wave begins. Don't exit too early ! In other words in order to go "20" consecutive, make sure you stay until the beginning of wave 21 - or longer.
You do not need to exit the game in order to get the 20 consecutive wave achievement to pop. As long as you do 20 consecutive in the same game, you should be good to go.
For practice, you can do what I did, and start the game on wave 12. I do not know how much inside each wave is scripted and doesn't change, so be on the lookout for anything.
Happy hunting !
-MI