Unity 2D sprite mask?

So I started using Unity a few weeks ago and I have this simple problem that I can’t solve.60084-captura-de-pantalla-2015-12-15-183333.png

I wanted to create kind of a portal in my game and I expect the asset to dissapear when it enters it. I’ve developed a few games in HTML5 where I could easily create a mask that would hide everything in an area (in this case “behind” the portal). But I can’t find a way to do it in Unity. Any help would be appreciated.

You can add a mask component to do this ( https://unity3d.com/learn/tutorials/modules/beginner/ui/ui-mask ) but I’ve had mixed results when dealing with curves, in which case creating a custom shader to handle the masking is your best bet.