Do you need more card ideas for the D&D Adventure System games?
That is a really good question, as cards committed to combat are no longer part of your hand (they become dice.)
Since the card says "Before Combat" it seems reasonable that you wouldn't have declared any cards that become dice, so your entire hand - including those cards you would have used to fight Krank - are the starting point for selecting a random card. This means you might catch a break and discards something you won't use in the fight against Krank.
This is a bit of a deviation from the Red General in Defenders of the Realm, which requires each hero to roll against the red cards they committed towards fighting the general (supposedly they are mesmerized into pulling their punches.)