Grass Roots, the Michael version, can be one of the trickier missions in GTA 5. The challenge is that if you stay in the position you start the mission, then the aliens attack from all sides and different heights making it hard to take them out in time.
However, in as all GTA games, there’s almost always an easier way to complete a mission and for this one you don’t even need to use any cheats. Start by taking out the first few aliens in front of you and walk forward as you do so towards the left of the rectangles next to the pillar.
Go through and stand to the left on the other side of the wall. Then turn around the aliens will almost all run to the same spot. Aim at head height and a single shot will do the trick. One or two aliens will try and sneak around behind you, so just keep an eye on the map for the red dots and swing around in time. This way you should be able to complete the mission with no real problems, as we show in the video below.