How to Create a Life Bar in PowerPoint

Method 1 of 2:

Draw up a rectangle somewhere in the slide.
Add effects. Now, animations/custom animation/add effects/exit/wipe. Click the drop down bar, then click from right.
Set it to after previous (which makes it go down when an attack has occurred), then choose the speed.

Method 2 of 2:

Draw up three separate rectangles, the click the last one (on the very right), then custom animation/exit/wipe/from right/after previous/then choose your speed.
For the other two, select the middle one, the custom animation/exit/wipe/after previous (make sure it is just after the first rectangle that goes down first by right click/show advanced time line/choose speed.
Then the last one, do the same, and then, make sure it's just right after the middle rectangle.