Chase down metal head beasts was a mission in Jak 3. Jak was looking for special precursor artifacts and Kleiver just happened to have sold one to a "nice band of Metal Heads". Together with Sig they chased after them to take it from them.
A on-rails shooter mission where you control the Gila Stompers turret, shooting down metal head beasts and metal head flyers as well as the bombs and missiles they each launch. Metal head beasts and metal head flyers will come in from all sides every so often and fire at you, forcing you to target their weapons to avoid being hit. It's not actually needed to kill all of them, just the very last metal head beast carrying the quantum reflector. The game will give you enough time to actually kill it, as you manage to close in on it back in front of Spargus.