My take on the concept... I guess I've fleshed it out (way) too much, but it's just an idea:
There would be a map with several regions - one for each element, but possibly other ones as well. Special deck building rules would apply to each region (50%+ cards of element in question for elemental regions, at least seven different elements in deck for rainbow region, etc.). In order to fight in a region your deck would need to fulfill these conditions, as would your guardian code (I'll get to that).
There would be three types of enemies in each region: AI3, AI5 and Palace Guardians. All of them would fulfill the regional deck restrictions as well. AI3 would be predefined (perhaps just one type in each region), AI5 would be Halfbloods (random cards, but fulfill conditions) and Palace Guardians would be like False Gods, except that their cards would not necessarily all be upgraded. Winning against opponents in a region would raise your score in that region (as well as regular score), while losing would detract from that score.
When fighting in a region you would first fight AI3, then AI5 (if your regional score was high enough), and finally Palace Guardians (if your regional score was high enough). If you lost you'd have to start over from AI3 (your regional score wouldn't be reset), and you'd also start over if you went to fight in a different region or refreshed the game.
Now about the guardian code: you could define a guardian on your deck building screen. You would do this by entering a deck code into the guardian window (which would be like the deck import window). You would have to have all the cards from the code in your deck and/or storage for the code to be accepted, and you couldn't enter a region if the code didn't meet that region's criteria. Defining a guardian wouldn't be necessary in order to fight in a region.
The server would keep a list of the players with the highest regional scores who would currently be fighting in that region and have a defined guardian. Whenever a new Palace Guardian would be needed in a region the server would check its list for that region: it would contact the account from the top of that list and fetch the player's guardian code. The player's regional score would be reset.
There would be X Palace Guardians in each region (all of them nameless). In the short time period when not enough player-made ones would be available in a region they would be built the same way as AI5 decks. The player-made guardians would have a few stats: wins, losses, and cards. Once a guardian would be defeated 300(?) times it would be replaced by a new one. The player who made the guardian would get a reward based on how many players the guardian had defeated before it got replaced. (The reward could be placed into the player's card storage directly, available through the quests button or via a code - since the player would need to be fighting in the region in order for his or her guardian to be considered they could be given a code after they completed their current battle.) Finally, a guardian's card stat would track the number of upgraded cards that have been won from the guardian so far. Once it reached one hundred (case for 300 losses for each guardian) all further spins would be made with downgraded cards only.
