Using an alpha/mask to drive effects

Hello!

I have attached a high end animation I am working on as an example.

I would like to do the following:-

1. have the coloured animation sequence (whether mp4s or exr sequence) as the backplate.
2. use the alpha/mask animation sequence for effect areas. In this example the glow would follow the white dot.

For the life of me I can't figure it out. Please a) tell me how stupid I am then b) explain what I need to do.

I would like to do this in the Colour panel rather than Fusion. But a tutorial for both would be great.

Thanks very much.
Tom

backplate

1.jpg (69.2 KiB) Viewed 412 times

effect mask

2.jpg (32.34 KiB) Viewed 412 times