Feed the Murk Puff 10 Guppos
During the fight with the Murk Puff it will eventually move into its shell and launch a bunch of green orbs at you. It will then stick its head out and there will be a prompt to shoot Guppos at it to get it back out of its shell. During the fight, you need to have this happen at least 4 times so that you can shoot 3 groups of 3 plus 1 more Guppo at it. This is the only world eater that you might really potentially miss the achievement if you do the fight too quickly because you deal a lot of damage with the vehicle if you are constantly shooting.