My friend Kymakazie - Character (worldofwarcraft.com) has the Whole-Body Shrinka’ effect randomly apply to his character while we play. It happens every so often anywhere in the world, even in instanced content with no other players around (it happened in the Black Temple sewers with just the two of us yesterday, for exemple).
My friend does not use any macros, so there’s nothing he uses that could embed activating the toy without his knowledge. AFAIK that would leave addons embeding the use of that toy somehow, but either of us use mostly common addons, nothing other people wouldn’t have encountered already.
We tried googling the issue but nothing comes up.