Gunstar Heroes

Relatively easy boss, however to defeat him without taking any damage just your jump attack (hit jump twice). This will hit him for a ton of damage. Use it again and again as he walks across the screen and it'll be dead before it even performs an attack on normal.

This achievement is easy enough, you'll unlock it by defeating the boss you encounter during the middle of the first level, you'll come to find that in Gunstar Heroes you're able to almost mindlessly run through the levels holding down the fire button.

The only thing that really matters is which weapon you choose to use, I'd recommend either the homing bullets (the small green arrows) or the flamethrower weapons, the homing bullets will take out enemies without you having to aim in their direction constantly while the flamethrower inflicts the most damage, you also have the ability so save whenever you want, make good use of that!

This entire game is incredibly easy to complete, watch the video below for a guide on this achievement.

* ^{Credit to SerenityWind the video}