The Marauders are the worst part of DE for me.
They can be downed with some strats, somewhat easily. But when they show up randomly, you can often kiss all your one-ups goodbye especially if they're surrounded by mobs. So that leaves you with nothing for the rest of the mission, unless you restart from the beginning.
The Marauders are the definition of interruption to game flow. Again, before anyone retorts me, yes they can be killed somewhat simply in ideal conditions without losing a single life. However, ideal conditions is rare/non existent in this game and a few of the Marauders spawn points are random.