Is the medallion being used in Haunt N21?
The errata added restrictions on this use of items:

If there are five heroes and a monster in a room, could each of them use, say, the Spear to attack that monster, then pass it on to the next person?
No. Add this rule: &quot;For each item, during a turn an explorer or monster that can carry items may only perform one of the following actions: use the item, give the item to another explorer, drop the item, steal the item, or pick up the item. Using the item means making any attack or roll or other action in which the item is involved in any way.&quot;

So the heroes cannot do this, due specifically to the last sentence: &quot;Using the item means making any attack or roll or other action in which the item is involved in any way.&quot; Even though you are not attacking with the medallion, as you would with the spear, the medallion is involved in the attack as it is a requirement for the attack to have any effect.