Is the mystery card "Molten Ash Golem"
If you combine silver with a vampire it turns into ashes.
This is a very cool analogy. However, it's not what I thought of. So Molten Ash Golem isn't the answer.
And yes, Silvershield Bard would have been too easy haha. The actual difficulty of the riddle is somewhere in between those two ideas -- not too complex, but not as straightforward.