Sigma Head

Sigma Head is the boss of the Intro Stage. It sends out energy spheres or a large beam from its mouth. After this boss is destroyed, Sigma's real plot is revealed. Also, Sigma Head turns into a purple miniature form and becomes a wandering virus. If X gets hit with it several times, he will get a condition that damages him for a while. If Zero gets it, he actually becomes stronger (mainly because he was the one who carried the virus before Sigma got it).