Combo Master Trophy
Get the Apocalypse Combo Kill Bonus (150 Kills)
This trophy is awarded for ending a kill combo above 150 kills. This can be earned basically at the same time as Keep It Up. You may earn both in your run of Endless mode, though they can easily be earned in Arcade mode on Braindead.
Credit to biggs for the following method.
You will be doing this on round 6 in Arcade mode, so first round take the money path, then after that alternate between weapons to get shocker, supplies to get autoturret, and two more money rounds to upgrade them. On round 6 you will want to go down the score path to the arena area with the conveyor belts with saw contraptions at the end. Drop a turret at the entrance then move up, activating the conveyor traps and dropping more turrets on the other side. What you will now want to do is take out your Shocker and move up to the top left by the exit gate to get the rest of the enemies to spawn. Now move back closer to your turrets and take out as many enemies as possible. If you need to take out your SMG to kill the Jumpers and a Cutter if one spawns, though watch for it's pod to drop so you don't get killed by it when it lands. If done properly you should be able to kill all the enemies in the arena and end up with at least a 150+ combo. This should also get your kills-per-minute above 100 as long as you ran through the level fast enough.
If you manage to get this on your first run through the score area without dying it should be very easy, as the Mouths that you ran past on the path should be outside the gate still spawning more zombies, which you can easily kill to up your combo. If you do die then it is slightly harder, but still very doable. If you lose your combo or kill all the enemies without reaching 150 just let yourself die so that you respawn at the entrance to the arena.