Mega Man 3
Gamma made its first appearance in Mega Man 3. During the first form, it has a small, blue head and Mega Man must use Shadow Blade or Hard Knuckle against the head and Dr. Wily will control Gamma with shots during its second form and then has eyeballs. In order to defeat it, Mega Man must use Search Snake or Top Spin to defeat Gama and finish the final battle.
Gamma has a peace symbol and has a smile and appears as a giant yellow ball robot and has blue details and then has the cockpit on its head where Dr. Wily controls.
Gamma only appeared in Asteroid Blues in Rockman Gigamix and later made a brief appearance in Metal Heart.
On Gamma's small head during the first form seems to have the Greek word for Gamma (Γ) on its forehead.