SplinterGroup
You could make a puzzle where the trick is to take it apart (ala Kel Snake). 
For packaging simplicity, the instructions could be placed inside. 
Or be like the originals... apparently they come without instructions.  
I've received a few green bum (grassy arse) PMs on my 3DW models from owners getting the solution... although there are already YouTube solution videos posted by others. 



 Steve Rasmussen 
Tis one looks complicated...
This is actually less complex than some of my easy looking ones.

If your first cut is too short... Take the second cut from the longer end... LBD