After you have your blocks drawn out, its time to emboss the blocks into the foam core. I used a wooden stylus, it is for sculpting with clay, I think I got it at Michaels. Any tool with a blunt tip will work.
You don't want the tool to be sharp because you do not want to puncture the outer paper of the foam core (notice I did in the bottom left corner below). A ball point pen will work well too. Take your stylus and rub back and forth over your lines to make a indentation in the paper of the foam core. Make it as deep as you can without puncturing the paper.
Then round all the corners of your bricks
Add some character - put as much or as little detail into it as you like.
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"It ain't about how hard you hit, but how hard you can get hit, how much you can take and keep moving forward - thats how winning is done!" Rocky Balboa