Horn Mask is a Black Cross Army Masked Monster. Aside from using a staff, his main ability is to transform himself into a rock, using it to give him immortality and to survive attacks such as the Gorenger Storm.
Horn Mask was the leader of a special corp of computerized Zolders transformed into human bombs, which he used when invading EAGLE bases to blow them up. Akarenger, Kirenger and Momorenger try to stop him initially, but he survives their Gorenger Storm and Ooiwa's anger ends up making him victimized by his human bombs. The Masked Monster soon tried to trace the Gorenger back to their base and attacks Snack Gon, with Ooiwa and Gon attacked without revealing the Gorenger or their identities before he left without any information. Kirenger follows Horn Mask but is further damaged by his human bombs.
With Shinmei's assistance, the Gorenger come up with a strategy to defeat Horn Mask. First with his human bombs, they use their machines to drive around to confuse their computers before they attack them. Then when they use Gorenger Storm, they set up a special version which drops a mini-ball during the final assault before it attacks Horn Mask. The Masked Monster survives the attack, but ends up walking on top of the mini-bomb, finally finishing him off.