Difficulty: Easy
A gauntlet is a set of missions. The first set is 6 missions and shouldn't be at all difficult for you. There's a nice array of weapons to gain as you go along, which makes this ridiculously easy. Personally, i used Barry, with a Pistol, Magnum, and Sniper.
Pick a character and play the first mission. Afterwards upgrade your weapons and character and play on. Rinse and repeat and the trophy will be yours in less than an hour.