Just looking for easy elf on the shelf ideas and the theme it follows so if my kid has similar interests I might steal your idea 
. (If you hate elf on the shelf thats fine, I understand! Just leave the thread.
Heres a few of mine. If any use:
Adopt me. Roblox - choose 8 random figures or teddies (preferably animals) and place them in 2 seperate piles. Elf leaves a note asking if it's a fair trade
Diary of a wimpy kid - get a cheese slice and rough it up. Position elf so it gets the 'cheese touch"
Minecraft - turn a bit of paper into a cube mask and colour it like a creeper. Place on elfs head
Ghostbusters - if you have a staypuft toy (or otherwise print a picture) put it under a cheese grater and have marshmallows lying around it.
Ghostbuster - slimer toy or photo with genuine green slime around it
If i think of more ive done I'll post them but feel free to add any you have!