For the "window" and the scalloped circle I used Nestibilities Dies in my Cuttlebug. The Hero Arts stamps are CG211, F5306 and CG157.
To view a Hero Arts video on masking, click here. For my masking, I stamped the Hippo on a piece of typing paper and cut it out. Then I stamped him on the inside of the card. Next, I applied the cutout version ("the mask") on top of him using removable adhesive. I then stamped the cupcake stamp (which actually has a heart on top) over the image, placing it carefully. I removed the mask and colored it all with Copic pens.
It sounds a little confusing, but really isn't. You just have to think in layers!
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The sentiments were generated on my computer and the ribbon, button and baker's twine are from my extensive stash.
I love the way it looks like the Hippo is standing on a grassy knoll until you open the card and see the cupcake surprise.