Robnos is a mamodo that likes picking on weak mamodos like Zatch. He considers himself invulnerable and uses his armor and helmet to absorb attacks and gather energy for his own spells. Not much is known about the two.
Rops and Apollo
At some point in the earlier days of the battle, they crossed paths with Rops and Apollo, and challenged him by firing at him with Biraitsu. Apollo's psychic abilities left them outmatched, and the battle ended with him nonchalantly pushing both of them into water without burning their book.
Zatch and Kiyo
They tricked Zatch and Kiyo to battle them in a freezer compartment room by making them think they kidnapped Suzy (due to the fact she was sick and hadn't shown up to school, but Zatch and Kiyo didn't know that Suzy was home sick). At first, Zatch and Kiyo have problems with Robnos because he could easily evade Zatch's Zaker. However, when Zatch hit Robnos and he falls near some boxes, Kiyo notices he got up with no wounds. Robnos uses the walls inside the chambers to make his first spell, Biraitsu, bounce around the place. Kiyo positions himself and Zatch on a part of the floor where no lasers could hit them, but lasers begin to hit Zatch no matter where he is. Kiyo destroys everything inside the freezer and hears steps on what remains of it. He realizes there wasn't only one Robnos but two mamodos battling against him and Zatch, what explains why Robnos survived unscathed to Zaker. When he tells what he recently discovered to Ruku and uses Jikerdor to immobilize the clone and attach him to the metal door at the entrance of the freezer, Robnos' partner casts Rei Buruk and he fusions with his clone. He seems tougher than before and Zaker no longer damages him. Zatch and Kiyo manage to win when Kiyo threw a rod in Robnos' helmet and Zatch shot a Zaker at it causing him damage and burning the spellbook.
However they revealed that they never kidnapped Suzy and merely created a statue of her and added a letter to lure Zatch and Kiyo, Before Robnos could completely vanish he informs Kiyo that a while ago he saw a mamodo in England that looked exactly like Zatch, leading Kiyo and Zatch to travel to England and try to uncover the mysteries of Zatch's past.