Defeat enemies with the vehicle, long gun, melee, and grenade, in that order, in 20 seconds.
Sounds crazy, right? Well, it can be done at the end of chapter 3 during the ruins encounter.
As soon as you start, there will be 2 enemies directly ahead of you, so run one of them down with your jeep. Then jump out and kill the other with a long gun, vault up towards the tower and melee the next enemy, then throw a grenade up into the tower to take out the 4th guy.
You can restart the encounter as many times as you like until you get it.
Make an Entrance
Defeat enemies with the vehicle, long-gun, melee, and grenade, in that order, in 20 seconds