Few beginner questions

Hello,

I have several questions about 2D games in general. I am making a 2D game for smartphones and I encountered few problems.

So my first problem is about using sprites. Let's say I have a sprite that contains an oval portal. Now I want to move another object that it looks like it moves through. What I tried so far is that I split that sprite in the middle, so that I can manually adjust the layer to get the effect I want. I guess that there must be another solution to solve such tasks.

The second question that I have is about setting the right resolution as well as creating sprite images for different devices and platforms. So basically I just need information about that topic.

I highly appreciate your answers.

 

So you mean like when the player stands in the portal, the alpha value changes transparency to look like he is in the portal? Why not make the portals alpha value change when the player enters the portals collider?
Maybe I am misunderstanding the question though.
I'm not sure I can answer your other question as I have no clue lol.