You need to make it to wave 100 and beat wave 100 to get this achievement in the co-op dojo. You will never be able to do this by yourself so You need to get 4 people and do this together and make sure that you do not collect 1000 tokens while doing it or the game will end. So if you are getting close to 1000 die a couple of times because each time you do you lose 100 tokens. You have infinite lives so don't worry about that. Make sure to always use monster tokens on yourself because if you don't you will be dieing every 5 seconds making it very long and tiring on yourself. This achievement will take about 2 hours if done right and 3 if not.