I was looking at putting together a few Worlds, but after some thought I realised that until we know how the Planeswalking Quest is going to function it's impossible to accurately gauge deck difficulty and challenge rewards. Is a hard deck supposed to be hard by the standards of a Block Constructed card pool? Modern? Vintage? Should a Challenge be giving random rares as rewards or power 9? Until there is some structure to the Planewalking Quest then different worlds will have wildly differing assumptions and therefore power levels. Also, I noticed that as long as old power cards are available in the general card pool decks will very quickly tend towards Vintage, which makes a lot of cards useless when you get them. Basically the power level of decks in Magic goes Draft < Block Constructed < Standard < Modern < Legacy < Vintage and it would be cool if your deck went through that progression than jumped straight to Moxen and
Necropotence.
The basic question is whether you should go through the worlds accumulating cards into a single deck that gets better all the time, or whether you should have to play each world by it's own rules and make a new block constructed deck each time. Whilst I can see the appeal of honing your favourite deck over time, I think that this way skips most of the content of the different Worlds. Once you level up to Hard you will only ever see Hard decks from any world you visit, missing out on all the flavourful tribal decks and such. Also, once you have a honed Hard deck then 95% of the new cards you get from a world will be worthless to you as they won't fit your deck's power level, which takes away a lot of the fun of getting new cards. This has lead me to a few ideas for the Planewalker Quest mode.
The Planewalking QuestYou should start in a world with a fairly restricted card pool, to entice the player to want to Planeswalk to the other Worlds. I'm thinking all the base sets from M11 onwards, as they've been introducing some interesting cards into the basic sets lately and it gives you a nice selection of basic cards. To start with the Worlds would be locked off, and would have to be Unlocked before you could travel to them. This could be done by paying a fee, like how Unlocking sets is done at the moment, however I was thinking it would be cool if Challenge rewards could include "Unlock a specific world". That way you could have (for example) a Mirrodin themed challenge in the main world that, if beaten, gave access to the Mirrodin world. At the point a World is unlocked you get given a starter pool of cards (just like your initial Quest starter pool) drawn from that world to start your World deck. Once in a world you can only use cards legal in that world in your Quest Deck, and you start facing Easy opponents again as you build up your deck for that world. This way each world provides a new experience. The challenges for a world would give tournament staples as rewards, and would be calibrated against block constructed decks. As you can unlock Worlds as challenge rewards, or using credits, you should be able to have two or three Worlds unlocked at a time, so getting stuck on a World or getting a crappy card pool should just mean you can play another World to build up some credits to buy some better cards.
The player will want something to do with the card pool they are ammassing from the different Worlds, therefore I suggest that there should be "Boss" Worlds that you can only unlock by beating multiple challenges in the basic Worlds. First there would be a "Modern" world populated by Modern Tournament winning decks that allowed decks from the whole Modern card pool and is unlocked by beating any 5 challenges. This would allow players to build a deck from cards they accumulated in the various Worlds. Then there would be a "Legacy" World that was unlocked by beating the Modern world. Finally there would be a "Vintage" world that would be the endgame. I was thinking that the Modern and Legacy worlds should have a chance of giving Power 9 as Challenge rewards to prepare you for the Vintage world. Then once you beat the Vintage world Challenges maybe you have an "end Boss" deck with like 100 life and starts with all the moxes in play or something ridiculous to give players some bragging rights and a feeling of closure when they can finally beat it.
So, just some ideas I was batting around. I know some of these aren't possible without some coding changes, which might be a barrier, but hopefully I haven't proposed anything too radical. If people want to just create a honed deck and refine it the standard Quest mode would still be available, this would cater to people that want a more structured and goal oriented experience. What do people think?