I'd like to toss this idea out here:
What if a series of a AI opponents were introduced/updated with AI-exclusive cards? AI-exclusive cards would be stronger than normal counterparts, and normally unobtainable - beating an AI with such a card will instead add a corresponding 'downgraded' counterpart to the spins. This could used to 'tweak' some AIs by giving them stronger cards to enhance/cover for their tactics/stupidity respectively. In addition, this could also be used to create event-specific cards for new quests (if Zanz ever gets around to them) that could add more detail to the battle (For example, if your quest is to go into a slum and recover some valuable artifact, you could have 'thugs' that have a chance to attack the opponent instead to symbolize conflicting factions.) Alternatively, if an AI needs to be intentionally weak (such as a tutorial or for a 'marathon' fight that involves consecutive AIs attacking you w/o HP and deck refreshing), weaker counterparts of cards could be given instead.
Not all of the cards need to be counterparts or obtainable, though - there's actually a whole row of 'blank spots' in the game's card codes that could be used for event-specific cards such as Holy Cow (which currently takes up such a slot). Used properly, AI cards could flesh out the game in greater detail and provide appropriate deck balancing when needed.
I was also considering a 'You are the Elder/False God' feature that lets you use 'AI-Exclusive' cards (with some restrictions, of course - I was thinking reduced rewards vs. AI/Arena and unusable in PvP1 or PvP2.
However, these cards could be accepted in the PvP search system as a way for Events to give an advantage to a team. In addition, they could still expand deckbuilding, providing people don't mind reduced electrum/card gain.)
In addition, Kamietsu proposed a 'Hard Mode' that I'd like to put in the OP of this topic
What if after a certain level you could choose to sort of play the game in 'hard' mode. Where upon activating(after you buy th eoption from the bazaar or something so you can turn it off and on) where all cards for all opponents are upgraded cards, some decks replaced by harder ones for the lower Ai so everything is more of a challenge. It would provide an interesting dynamic to the game that might encourage more experienced an dhigher level players to play some of the lower AI for a challenge/cards instead of just spamming them for some easy score or the like. And of course the rewards should be upgraded too.
I propose the idea should be called 'Ascended' mode, with AIs getting stronger versions of their trademark cards as 'Ascended' cards. In addition, an 'Ascended' mode could upgrade the FGs to AI7 (aka 'True Deity/'Real God'/etc...), allowing Zanz to add a whole new level of difficulty to the game by just modifying already existing features. (Rewards would also be adjusted accordingly.)