The Megalith Beast is the boss of the "Tycoon Wil" scenario of SaGa Frontier 2.
When Wil Knights and his friends go to Weissland, along with Labelle and her brother william, they go into the Ice Megalith to explore the place and discover its secrets. They find a large pillar structure on the center of the Megalith, which causes a headache on them and make them faint. They eventually wake up, but William went there alone to look on the pillar again. Wil tries to warn him to stop, otherwise his Anima would be consumed, but he is too late, as William have his body mutated into the monstrous Megalith Beast, which immediately attacks Wil and his group. They keep the beast busy enough to flee the place. As they cross the ice bridge that connects the Megalith with the land, the bridge collapses, leaving the beast trapped inside the Megalith.
The Megalith Beast can be fought again anytime as a optional boss.