These creeper marshmallows from Minecraft were for the goodie bags at my son's 12th birthday. (You can see the cake from the party here.)
I bought square marshmallows at the store and airbrushed all sides green. It didn't matter if they were covered really evenly because the video game has that pixel-y look anyway. After they dried I used a black edible marker to draw the creeper faces on them.
I thought they were pretty cool, and they kids all loved them. :)
(I created my animated name at this site.)