[Clipper]

The way the card is worded, I'm pretty sure you roll both Blue Jumbo d6s regardless of how many dice you would be rolling otherwise.

The wording is definitely clear that the result on either dice can replace any regular die roll. The type of dice does appear to be irrelevant. Consider that the power can be used when searching too, or at any other time you roll a d6.

In a combat with your own monster/s, you roll once for yourself and once for your monsters. You don't roll them all at the same time. You'd be able to roll the Jumbos both for your roll and the monsters' roll.