Here is the full list of all 115 Final Days achievements.
Survive day 7 of the Last Stand Training's Over map on Recruit difficulty
Survive day 7 of the Last Stand Training's Over map on Veteran difficulty
Survive day 7 of the Last Stand Training's Over map on Elite difficulty
Survive day 7 of the Last Stand Training's Over map on Suicidal difficulty
Survive day 7 of the Last Stand Hospital map on Recruit difficulty
Survive day 7 of the Last Stand Hospital map on Veteran difficulty
Survive day 7 of the Last Stand Hospital map on Elite difficulty
Survive day 7 of the Last Stand Hospital map on Suicidal difficulty
Survive day 7 of the Last Stand Compound map on Recruit difficulty
Survive day 7 of the Last Stand Compound map on Veteran difficulty
Survive day 7 of the Last Stand Compound map on Elite difficulty
Survive day 7 of the Last Stand Compound map on Suicidal difficulty
Complete the Depths campaign on Suicidal difficulty
Complete the Escape campaign on Suicidal difficulty
Clear the 50th floor of the bunker in Eradication mode on Recruit difficulty
Clear the 50th floor of the bunker in Eradication mode on Veteran difficulty
Clear the 50th floor of the bunker in Eradication mode on Elite difficulty
Clear the 50th floor of the bunker in Eradication mode on Suicidal difficulty
Clear the 50th floor of Bug Hunt in Eradication mode on Recruit difficulty
Clear the 50th floor of Bug Hunt in Eradication mode on Veteran difficulty
Clear the 50th floor of Bug Hunt in Eradication mode on Elite difficulty
Clear the 50th floor of Bug Hunt in Eradication mode on Suicidal difficulty
Clear the 40th floor of Bug Hunt in Eradication mode on Recruit difficulty
Clear the 40th floor of Bug Hunt in Eradication mode on Veteran difficulty
Clear the 40th floor of Bug Hunt in Eradication mode on Elite difficulty
Clear the 40th floor of Bug Hunt in Eradication mode on Suicidal difficulty
Clear the 40th floor of the bunker in Eradication mode on Recruit difficulty
Clear the 40th floor of the bunker in Eradication mode on Veteran difficulty
Clear the 40th floor of the bunker in Eradication mode on Elite difficulty
Clear the 40th floor of the bunker in Eradication mode on Suicidal difficulty
Clear the 25th floor of Bug Hunt in Eradication mode on Recruit difficulty
Clear the 25th floor of Bug Hunt in Eradication mode on Veteran difficulty
Clear the 25th floor of Bug Hunt in Eradication mode on Elite difficulty
Clear the 25th floor of Bug Hunt in Eradication mode on Suicidal difficulty
Clear the 25th floor of the bunker in Eradication mode on Recruit difficulty
Clear the 25th floor of the bunker in Eradication mode on Veteran difficulty
Clear the 25th floor of the bunker in Eradication mode on Elite difficulty
Clear the 25th floor of the bunker in Eradication mode on Suicidal difficulty
Complete the Rendezvous campaign on Suicidal difficulty
Survive day 7 of the Last Stand Crossroads map on Recruit difficulty
Survive day 7 of the Last Stand Crossroads map on Veteran difficulty
Kill 250 mutants using pipe bombs
Complete the Rendezvous campaign on Elite difficulty
Kill 500 mutants using Spread Shot ammunition
Complete the Escape campaign on Elite difficulty
Kill 1000 mutants using Heavy Auto ammunition
Kill 50 mutants using your fists
Kill a mutant with a pipe bomb after you've died
Survive day 7 of the Last Stand Bug Hole map on Recruit difficulty
Survive day 7 of the Last Stand Bug Hole map on Veteran difficulty
Survive day 7 of the Last Stand Bug Hole map on Elite difficulty
Survive day 7 of the Last Stand Bug Hole map on Suicidal difficulty
Kill 9001 mutants
Kill 750 mutants using Spread Auto ammunition
Kill 250 mutants using High-Ex ammunition
Kill 500 mutants using Power Shot ammunition
Kill 1000 mutants using Rapid Fire ammunition
Kill 250 mutants using exploding barrels
Kill 250 mutants using Hot Shot ammunition
Complete the Depths campaign on Recruit difficulty
Complete the Depths campaign on Veteran difficulty
Complete the Depths campaign on Elite difficulty
Complete the Escape campaign on Recruit difficulty
Complete the Escape campaign on Veteran difficulty
Kill 1000 mutants using standard ammunition
Spin clockwise 33⅓ times in a row
Give ammo to another player
Complete the Rendezvous campaign on Recruit difficulty
Complete the Rendezvous campaign on Veteran difficulty
Kill 1000 mutants
Beat a mutant to death using your fists
Ignite 20 mutants with a single Hot Shot round
Kill 10 mutants with a single pipe bomb
Kill 20 mutants with a single pipe bomb
Kill 10 mutants with a single exploding barrel
Ignite 10 mutants with a single Hot Shot round
Survive your first day of the Rendezvous campaign or Last Stand mode
Kill 5 mutants with a single exploding barrel
Kill 99 mutants
Complete the Intro campaign
Kill yourself and a mutant with an explosive
Kill a mutant with an exploding barrel
Use an explosive to destroy a wall
Complete training
Survive day 7 of the Last Stand Crossroads map on Elite difficulty
Survive day 7 of the Last Stand Crossroads map on Suicidal difficulty
Survive day 7 of the Last Stand The Wall map on Recruit difficulty
Survive day 7 of the Last Stand The Wall map on Veteran difficulty
Survive day 7 of the Last Stand The Wall map on Elite difficulty
Survive day 7 of the Last Stand The Wall map on Suicidal difficulty
Survive day 7 of the Last Stand Hotel Floor map on Recruit difficulty
Survive day 7 of the Last Stand Hotel Floor map on Veteran difficulty
Survive day 7 of the Last Stand Hotel Floor map on Elite difficulty
Survive day 7 of the Last Stand Hotel Floor map on Suicidal difficulty
Survive day 7 of the Last Stand House map on Recruit difficulty
Survive day 7 of the Last Stand House map on Veteran difficulty
Survive day 7 of the Last Stand House map on Elite difficulty
Survive day 7 of the Last Stand House map on Suicidal difficulty
Survive day 7 of the Last Stand Car Park map on Recruit difficulty
Survive day 7 of the Last Stand Car Park map on Veteran difficulty
Survive day 7 of the Last Stand Car Park map on Elite difficulty
Survive day 7 of the Last Stand Car Park map on Suicidal difficulty
Survive day 7 of the Last Stand Duplex map on Recruit difficulty
Survive day 7 of the Last Stand Duplex map on Veteran difficulty
Survive day 7 of the Last Stand Duplex map on Elite difficulty
Survive day 7 of the Last Stand Duplex map on Suicidal difficulty
Survive day 7 of the Last Stand Mall map on Recruit difficulty
Survive day 7 of the Last Stand Mall map on Veteran difficulty
Survive day 7 of the Last Stand Mall map on Elite difficulty
Survive day 7 of the Last Stand Mall map on Suicidal difficulty
Survive day 7 of the Last Stand Graveyard map on Recruit difficulty
Survive day 7 of the Last Stand Graveyard map on Veteran difficulty
Survive day 7 of the Last Stand Graveyard map on Elite difficulty
Survive day 7 of the Last Stand Graveyard map on Suicidal difficulty
Kill 25000 mutants