I used to make nitrogen triiodide instead. A lot easier to make, but quite unstable.
Dropped it in small quantities, near the door to the chem lab and when people stepped on it, it would go off with a loud bang and a purple cloud.
To the OP:
Sorry for the digression.
Mercury is very hazardous. If you can't find where to sell it, please contact your
nearest Hazmat unit to ask about proper disposal.