One of the things that's most frustrating for friends I've introduced to this game is the amount of grind it takes to develop a healthy catalogue of cards, and that's a gap that only grows with each new introduction. It's just hard to get up to speed without spending an enormous amount of time playing.
The game already already has a fairly well established risk/reward curve though. If you risk more electrum, the rewards are potentially much higher. Most of the advice to new players revolves around developing a good lvl3 or top 50 grind deck, since that's the very edge of the risk/reward envelope that can be reached and operated profitably quickly. From there it's false gods, ideally with a deck good enough that the player can regularly pull in upgraded cards. Again, following the risk/reward curve all the way to the edge.
I propose an extension of the curve in the form of a new PVP mode. Entry fee for each game would be 30% of your electrum balance or three relic cards (not refunded). The winner would get four spins and would be able to win upgraded cards if the other player was using them. There would be no electrum reward for winning. The score bonus for winning would be very high as well.
Clearly this is not the sort of thing you could grind. In fact, it's a negative sum game as far as electrum is concerned! In fact, this isn't the sort of thing a well-established player would touch. For a fairly new player though with just enough cards to make a rainbow rush deck, the ability to get upgraded cards that easily would greatly shorten the path to getting upgraded cards for that god killer or PVP2 deck they always wanted. It would also give the relic card a purpose that doesn't make nymphs grindable.