edited my previous comment,to get combo,u can try Vault Defense wave 5,buy "start with random weapon],then use grenade launcher[restart until u get it].place your cursor on the path which is like letter "c"
finally,i got all badges.for b5,use c4 as a decoy plant all at bottom right corner,hide behind box[centre of the map]. 1.if 1 enemy comes,kill with melee[dont use gun] 2.if too many enemy come,detonate 1c4
b5 killing floor,insane mission.keep running and the u're surrounded by a ton of enemies. keep running and shot everyone u met,and then u're shot from every direction.sucks
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