I guess here's a little tutorial:
Layer styles used:
http://prntscr.com/82xs9p
Step 1: Get a white background
Step 2: Get Galaxy background and put it above the white background
Step 3: Pichu background, it helps if it's a png so you don't have to remove the white/black in the background
Step 4: Hold option and click on the the little thumbnail icon that pichu is in:
http://prntscr.com/82xtn1 (the box). When you do it though, you should see your cursor and then a little white box right beneath it.
Step 5: After you have clicked on that little thumbnail that i said in step 4, the pichu should be selected. Then go to the layer with the galaxy and click on it.
Step 6: Click on the magic wand tool and right click, then go to select inverse. It will look like this -
http://prntscr.com/82xuna
Step 7: After you have selected the inverse, click backspace or delete.
Step 8: go to the pichu layer and put it on overlay
That's it. Show me how it comes out
Look at my method, let me know what you think. That's what i did