MArcomage

Same keywords? What does that mean? What if one card has two keywords? It is upgraded to card that has same keywords (all of them)? What if such card does not exist?

I also wonder what happens to rare cards.

I think with more keywords in one card, either of them can be drawn. So a common "undead, holy" (yes, I know there isn't such a card) can resault in a holy card, a undead card, or a "undead, holy" card.

That Undead Holy card could probably be upgraded to other mixed keyword cards, too, like Undead Nature or Holy Frenzy.