Mystery boxes can be obtained from the Quiz Master random event. Players can choose between 1,000 coins or the mystery box upon successfully completing the event. Multiple Mystery Boxes can be owned at once, and they can be banked.
Examiner - OSRS Wiki
OSRS: How to Find the Stale Baguette in Old School RuneScape - Prima Games
Puzzle box - OSRS Wiki
Puzzle box - OSRS Wiki
Research package - OSRS Wiki
OSRS Murder Mystery - RuneScape Guide - RuneHQ
Pillory - OSRS Wiki
Music - OSRS Wiki
Fancy dress box space - OSRS Wiki
OSRS Beginners Guide - Everything you need to get started - OSRS Guide
Mystery box, Old School RuneScape Wiki