Biolizard

In the Sonic the Hedgehog fictional universe, the Biolizard was an early version (in other words, a prototype) of Project Shadow, a government project run by Professor Gerald Robotnik that was intended to create an "Ultimate Life-form" as a first step towards humanity discovering the secret of immortality. The Biolizard was a prototype of this "Ultimate Lifeform", and before it was closed down approximately fifty years before the events of Sonic Adventure 2, Project Shadow produced a more advanced being: Shadow the Hedgehog.

When the Guardian Unit of Nations came to space colony ARK in order to put a stop to Gerald Robotnik's plans, they found the Biolizard and shut it down. It didn't go without a fight however and it destroyed almost the entire group of G.U.N. officers.

The Biolizard remained in suspended animation aboard the ARK until Sonic the Hedgehog and his crew came. After Sonic stopped Doctor Eggman from destroying Earth, a video of Professor Robotnik came online warning people of Shadow. Sonic and Eggman joined forces and helped to deactivate the Eclipse Cannon.

But when Sonic and Knuckles entered the cannon's core, the Biolizard was awoken and pulled ARK into Earth's atmosphere, causing it to fall. Amy Rose convinced Shadow to help save the Earth. He remembered the last wish of his childhood friend and Robotnik's granddaughter, Maria Robotnik, and helped Sonic and Knuckles get to the Chaos Emeralds. Though Shadow managed to defeat the Biolizard, it used Chaos Control, and fused with the space station itself, becoming the Finalhazard. It was finally destroyed by the combined power of Super Sonic and Super Shadow, though Shadow used the last of his strength to prevent the Finalhazard from crashing into the planet, and fell to earth.

Some fans believe that the Biolizard's body fell from the ARK and is now in the Black Arms' Black Comet, which was destroyed by Shadow.