To do this cheat you need two people. Both have to be in seperate helicopter.

Both people need to fly at equal heights in a beacon laser. Then both people need to fly down at equal height (at least 10 feet under the beacon).

So when you kill enemies you get agility with firearms or explosives (depends on the helicopter that you have).

But if one of the players goes higher or lower then the other the cheat won't work.