These effects improve on my first Final Cut Pro X effect, ‘Mask 8 Points.’
The current version of Final Cut doesn’t allow keyframing of mask shape co-ordinates in effects. These effects (which come in 4, 8 and 16 point variants) add transform controls to the mask (like my 8-point matte effect for Final Cut Pro 7).
The default effect:
With the mask points scaled, repositioned and rotated:
Drag the transform control to reposition the mask, drag on an edge to scale, drag on a corner to rotate.
Here are the controls: