How to make a simple mask like in Hitfilm? So, I want to use Blender for motipn graphics, and I previously used Hitfilm Express. One of the most frustrating things in Blender is creating a mask. But how does one do that like in Hitfilm? In Hitfilm, you literally just add a mask in the properties of something, and then thats it. How does one do that in Blender? 

And I want to know how do I make the mask transparent without using a color key node (right now to make the mask transparent, on the mix node, I put the background to be green, then I use the color key mode to make it transparent)
You can use Set Alpha node(In Converters) and as an Alpha input use the mask. You can also use Alpha Over node with Alpha 0 background input and your image "over" input, but that leaves sometimes ugly rim, so the first option is better in most of the cases.