This achievement can be done solo or coop. Needed complete the descent easter egg to unlock D.F mode. I hit a couples of tips to reach round 20 on hardcore mode in descent. If you down when you finish the easter egg, you can enter in the hardcore mode at the being of the game, when you respawn in the building behin you are locate a device, push it and you will enter in the hardcore mode
knife if you can because you only grab points after kill. Hitmarkers not count points. Punch with exo too.
2-I recommend 3d malfuction weapon
s because if you try with hbra this weapon isnt good than ak12, omn, ameli, pitapek etc. ( In my second try i made it with ak12 mk 14 and the KL03-Trident mk 5
3-Stay at the desinfection room because it is the best place to spin up zombies to make high rounds.
4- In dogs
rounds Just Kill all and recover your full ammo.
5- In infections
rounds try to not take damage because if you will infect you need pay to desinfect, stay jumping constantly near the desinfection room.
6- Perks i own in my try: Exo health, Exo Reload, Exo Stockpile and Exo Soldier
at the round 19 because in the last fight with oz you need it.
7- In the second fight with oz you needed a good weapon to kill him at the four spots when the windows will open, i recommend a LMG or AK12, S12
is good for kill him
8- The last battle, i recommend when you enter in the oz room, fastly active the 4 generators, i recommend EVER
surround the map because when you desinfect oz you can shoot to him for a short time, when you see the hitmarker run to the most near generator and active it and run to the other and same because it is more important in this battle.
I hope this helps