I'm trying to make an intro and have a polygon clip. The thing is, I have this text that scales from 0 to about 1000 percent so that the white letters will completely cover the screen. Then I have this one round object that currently has a red color (This is the object I want to change to be invisible) which also scales from 0-1000 percent. What I want is the round object to cover all the existing layers and fully covering the screen, overlapping all other layers but still being invisible so that I can place another clip behind.
The answer in Track Matte. Put your round object above the layer you want to mask, and select Alpha Matte from the TrkMt selection of the below layer. If you need to mask out several layers, precompose them first.