Koral Q (コーラルＱ, Kōraru Q, also "Coral Q" but translated as "Koral Q" in the English Viz manga) and Grubb (グラブ, Gurabu, translated as "Glab" in a fan scanlation of Zatch Bell! The Card Battle) are a team encountered by Zatch and Kiyo. Koral Q has the rare ability to detect other Mamodo, and using this they have been spying on Zatch, his friends and the other Mamodo. Koral Q only refers Kiyo's name as "Piyomaro" (Kiyomaro Takamine). Before meeting Zatch and Kiyo, Grubb was the way Kiyo was before meeting Zatch: High IQ, friendless, and no interest in making friends with anyone.
After Koral Q finds Zatch, Grubb creates a mechanical flying yellowtail in an attempt to attract Zatch and Kiyo to a bridge under construction, where they surprise Kiyo with a laser spell (Roboruga) and destroying part of the bridge, turning it to one with no exit. Koral Q reveals that he and his partner studied and researched many of the mamodo and even the 1000 Year Old Mamodo so that no one could defeat him. After a few tests, Kiyo thinks that he's lying, but Grubb starts using a series of spells that cancel theirs (they use Zakeruga, but it is reflected with La Robogargu). Angry of the fact that Koral Q had knowledge of the evil that Zofis was doing, and then did nothing to help, awakened Zatch's ability to read his opponents' attacks. This created an opening to land a hit with Zagurzem. Kiyo eventually figures that Zagurzem has a secondary effect that allows the creation of "chains". Kiyo uses the mirrors of Ganjido Roboron to form a chain and power up Bao Zakeruga. With the defeat, Koral Q then reveals some information about the strange huge structure from the Mamodo World and fades away, leaving Grubb alone. Back at his school, Grubb then starts making friends as Koral Q requested.
Koral Q is a robot-like mamodo who has an ability to sense the presence of other mamodo, even if they're on the other side of the world. However, Grubb uses his incredibly high IQ to do research about each mamodo, and then get its weak points or see how strong it is. Grubb is an extremely smart teenager who thinks that everyone else is "trash" because he's the smartest one, but after Koral Q's loss he start making friends.
Description: Koral Q transforms into a strange flying mirror-like object that can generate mirror shields used to defend or attack.
It is possible that Grubb's overall character design is based off of the titular character of the series, Dexter's Laboratory, this is possible due to his attitude, red hair, glasses, genius IQ despite his age and working with a robotic partner.
This could be a simple coincidence but Koral Q resembles the character Gir from Invader Zim:
They are both small robots.
They are both loud-mouthed, eccentric, and obnoxious.
In Koral Q's song ("Coral Q no Henkei Taisō"), he is seen hitting his head with both his fists something that Gir did in the first episode of Invader Zim.
In the anime, Arth debuted before Koral Q, while the opposite occurred in the manga.