I've had the game since it came out and I still don't have this achievement. I've tried many many times but I just can not seem to get to 50k. I usually do it with one other person. The main problems are the bosses. The one with the Penetrator often one shot kills me from far away. Also, when trying to go for Team Whiplash, I often only get Bossed on its own which is worth less points. I buy all the defense and speed upgrades but still get downed in a few hits by the regular enemies. I try to do the strategy where you leash enemies into the tornado with your partner, but it's pretty tough on wave 20 with all the bosses. I was just wondering on a couple of things. Do you guys think it would be easier with 2 or 4 people? Also, is it worth using any weapons apart from the PMC and the Flail? Any other tips that worked for you guys?
It's embarassing really as I know of a few people who got to 50k the day the game came out. I still don't have it, lol.