Lord Mantid emerges as the primary antagonist across the Spider Riders narrative. This ancient evil entity, affiliated with the Hell Councils, endured imprisonment before fellow council members secured his release to wage war within the Inner World. His central objective focuses on collecting the four Oracle Keys—fragments of the Spirit Oracle's power—to dominate Arachna and eradicate humanity.

Originally human, Mantid harbors deep resentment toward the Spirit Oracle. He blames the Oracle for depriving his Invectid race of sunlight and vegetation, fueling his genocidal campaign against humanity and driving his manipulation of the Invectid armies. Mantid commands through fear and deception, directing his high-ranking generals, the Big Four—Buguese, Stags, Beerain, and Grasshop—to orchestrate invasions and retrieve the Oracle Keys.

Mantid's tactical prowess manifests in long-term schemes. He exploits Aqune, an Oracle Handmaiden placed under mind control, to locate and steal the keys. After securing multiple keys, he merges their power with Aqune and an Ultimate Machine-Sector, intending to drain Hunter Steele's keys and unleash destruction. His actions culminate in plunging the Inner World into darkness using two keys, neutralizing Hunter's abilities temporarily.

Mantid's tyranny, however, erodes loyalty. Generals Stags, Buguese, and Beerain eventually defect upon recognizing his nihilistic goals. They protect the Spider Riders during Mantid's final assault and deliver the remaining Oracle Keys to Hunter. In the decisive confrontation, Hunter defeats Mantid using the combined power of the keys, restoring sunlight to the Invectid Nation for the first time in centuries.