Not much is known about Nightnubs, aside from the fact that he's a wizard who derives his magic from drinking Poop Cola and wants to destroy the world. As such, he's an enemy of Poopwatch, a secret society of wizards who protect the secret of Poop and oppose those who would misuse its power.
Nightnubs first appears in Issue 29, when he attacks Dib, who has just tracked down a bottle of limited edition Darkpoop for his sister. Nightnubs tries to take the Darkpoop from Dib, but is attacked in turn by Poopwatch member Fizzmitz. The two fight, each using various flavors of Poop to power their magic, until Nightnubs finally gets ahold of the Darkpoop. He then flees.
By having Dib drink many different flavors of Poop in order to give himself a sugar rush-induced mystical vision, Poopwatch learns that Nightnubs plan is to use the Darkpoop to summon Poopthulhu, a giant monster version of Poop Dawg, in order to destroy the world. To stop him, Fizzmitz assembles a group of Poopwatch's members to attack Nightnubs' lair while Dib retrieves another bottle of Darkpoop to counter the one Nightnubs is using to power his summoning ritual.
However, Dib is so delayed in getting ahold of the Darkpoop, that Nightnubs succeeds in summoning Poopthulhu. This forces Poopwatch to fight him head on, ultimately succeeding in defeating Nightnubs and Poopthulhu, saving the world.