So these are the new cards by class they are going to release with the expansion/patch. When it comes to mage they introduce a new secret.
Duplicate: When a friendly minion dies, put two copies of it in your hand.
At first sight one might think 2x Yeti/Cairne/ ect but a single polymorph/hex would be more than enough to ruin your plans and pretty much waste your perfectly deployed secret by giving you two awesome 1/1 or 0/1 + taunt creatures. Maybe in a secret heavy deck this secret might find some use if one is able to drop before hand a CS or Spellbender but that means that the secret deck becomes even more gimicky by relying on optimal draw situations.