The Mig-21 is featured in nearly every combat training mission as a basic enemy.
The Mig-21 can be selected as a wingman aircraft in Missions 1 and 2. It is also a very frequent hostile fighter in the first seven levels, and is very easy to destroy. Meanwhile, if Gargoyle 2 is given a Mig-21, he does not perform too badly in it, especially in Mission 1.
The Mig-21 is the first aircraft available to fight in Dogfight Mode. The hostiles are easy to engage, as there aren't that many jets to fight.