Deathmatch mode is an alternate form of gameplay. There are three challenges to choose from.
1 - Earn a million: Pretty self-explanatory. Collect a million dollars ASAP. Best to do it in Qubba.
2 - Kill 'em all: In 1 month, kill as much robbers as you can. I recommend to sell shoes in Verdammter Platz once and buy an M4 or AK-47 and to hire some help with sniper rifles.
3 - Survival mode: Survive as long as possible.