Sorry.
The arena balance changes have made it almost impossible to get a 50-wave achievement. I understand that removing the achievement was not the best solution.
I have decided to create a wall of fame for those who have earned this achievement. Write in the comments to this post if you have earned one of the "50" Achievements. I will create a wall of fame in the arena and in the menu where I will mention all the heroes.
I hope you can forgive me.
Thank you for playing Force Reboot.