You mean the 3 or more kills 20 times or the pvp one? The pvp one is super easy ( c wot I did thar) cause if you don't panic mode a super ad use it properly you can get more that 1 kill and since you get 3-4 supers in a match you can knock it out in 3-4 matches, I usually do as a gunslinger. And the pve one is just as easy just a little bit more time consuming. Just need to find a spot in the cosmodrome and go crazy. There is quite a few spots you can pick where there is enemies around and one pack that always has a bunch grouped up, skywatch is a good spot. I mean yeah the reward sucks but it's better than nothing right?

3 Or more pve.