Access the Garbage Mask menu from the Modular Keyer or the GMask node when you want to use multiple garbage masks or use the Tracer for detailed masks.
To access the garbage mask, use:
Batch, then select a node from the Node bin.
Timeline, then use Batch FX (see Creating Batch FX).
Timeline, then add Timeline FX from the Effects ribbon (see Adding Timeline FX).
When you access the GMask as a Timeline FX, you can enable Use Matte to use the matte input as part of the effect processing.
Tools, then select from the menu (See Accessing Tools).
The Modular Keyer, then select a node from the Node bin.