I currently have a basic shooter game where a point is added when you hit a bird sprite with the ball sprite. How do I add in a second bird sprite that if hit would end the game(or subtract from score). I also want to be able to turn this second sprite on and off when needed. Thanks in advance!

Make another bird, have it fly around similar to the way the other flies. In stead of adding a point subtract a point when it is hit.

change [ score] by (-1)

You can have another sprite that says game over. If score is less than zero show else hide.

You would use hide and show to turn the freindly bird on and off too but you will need to decide when you want it hidden or shown.