A good beginner difficulty mode is "You start with shotgun and jetpack."
I would argue that this is not "good for beginners." A "training" mode, if it existed, should teach you how to play the game. This suggestion would essentially teach you how to play a different
game, where your attacks have recoil and your jumps can send you flying. It's more like a cheat mode, really, and would be confusing for new players.