D-Rex

D-Rex is the boss of the third section of Sigma Palace in Mega Man X. It was supposed to be a large Mechaniloid based on the T-Rex (hence the name), but by the time the fortress was discovered by Zero, only the head was completed, forcing Sigma to convert it into a tank.

Its top can detach from the bottom, hovering in the air, and both try to crush and seriously damage X. When either section collides with a wall, it can daze X and knock him off. Both sections can also charge up massive electron spheres that inflict devastating damage. Its main weakness is the Boomerang Cutter.

D-Rex (Command Mission)
In Mega Man X: Command Mission, the D-Rex is a common, but powerful, enemy that appears in the Vanallia Desert. This D-Rex is a brownish-grey and is more dinosaur-like in appearance. D-Rex attacks with shots, Heterostorm and releases explosive miniatures called Mini Rex. If its mouth is damaged, it will be unable to release miniatures.

D-Shark
D-Shark is a weaker and more colorful version of D-Rex found at the Tianna Camp in Mega Man X: Command Mission. D-Shark attacks with Ultra Blizzard and releases explosive miniatures.

A D-Shark is available from the beginning in the Deployment Center.

Archie Comics
When Sigma-1 built an army of Mavericks to defend his base on the Lost Hex in Worlds Unite, the D-Rex appeared alongside such constructs as Eregion, the D-1000, Raider Killer, and the Shadow Devil.