It's in the US rulebook, Quest 2 the Cold Halls.
Also my thoughts on Rust. In my rules the spell is renamed Decay, as it can affect any item the heroes have. This includes magical items. I use my discretion as EWP as to whether a magical or non-magical item it selected. If I want to destroy a magical item, then a combat die is rolled. On a skull, the item's magic is drained from it. Gives options for removing items which I feel have overstayed their welcome or to give the player something to aim for again. Toying with letting them restore the magic in some (costly) way, but I will probably expect them to go find a new toy to play with as I have tonnes of items on my treasure tables.
I give the Decay spell to the odd minor creature here or there: a goblin shaman here, a fimir sorcerer there, a chaos sorcerer acting as lieutenant to a boss, etc.
I also have decay zombies which the heroes need to kill at range. On a successful hit, the hero is affected by the Decay spell.
Saiya
