Space Invaders Extreme

On Stage 1, there are four rows of eight aliens. Shoot four of them to get the Laser powerup, then sweep the remaining aliens with the laser.

This is just about as easy as it gets. Just make sure to kill enemies fast and a combo will build up. If you kill 4 enemies with the same color in a row you'll get a power up. Getting one of these in the the first level will almost automaticly get you this achievement. If you get the laser (light blue enemies) you can just hold the fire button and scroll right throu everything :-)