I was trying to think of what a Troll would eat and thought about "The Three Billy Goats Gruff." The goats tricked that troll. Now, trolls eat the candy to remember what happened and never get outsmarted again. Silly, I know - but I thought I would give it a shot. I think you're right about it being random. I used microsoft picture it 99 (old, I know - but I like it).
Here are my designs....
The Tr-olly Pop
I ~REALLY~ like this and hope it wins! It would get MY vote... gosh people are SO creative!