I hadn’t thought about render passes until Annabeth mentioned it and I found them a real time saver. I could render out different layers at a time to then layer back up in After Effects, making sure you export Alpha. This meant I could add things like smoke and mist in the foreground or background etc with out making an animated mask saving loads of time.

so for the shot below i rendered out the back ground separate, the table separate and the back alien and front alien separately.

This allowed me to but a layer of particles in the background and another in the foreground and some mist at the foot of the table. If I had done it using masking it would have taken so long.