I could see a pack having a chance for a rare... or some deal where with every 2-3 packs you buy you get a rare. But the problem there still is if you don't put out enough new spirits a person with enough money can basically buy their self an amazingly powerful dungeon.
And I would, if at all possible, avoid a scenario where he who has the most money has all the toys.
But you also have to make money too.
I could see having packs of cards that are only flatlands/drylands, or other combinations like that. I dunno... it will be a work in progress... and it will need to be fluid with the current gaming situations.
But first I hope Mom is having some luck with a programmer.
Neo, I've played a lot of different CCG's. Some of them are pretty good at minimizing the Pay-to-Win (P2W) scenario of "he who has the most money has all the toys".
Remember, 256 out of 506 of the spirits currently in SW are Rare or Ultra Rare. As long as you limit how easily/quickly someone can earn/accrue rares, then I don't think it will get out of hand. Even if someone can buy a pack that is guaranteed to contain 1 rare/ultra card, they'd still have to buy hundreds of packs (probably ~$1000) to get them all. Also, remember that currently a lot of the rare cards aren't that great/powerful, so getting an ultra rare card doesn't mean that you're automatically getting an extremely powerful card like Diana/Baldur/Grim Reaper, you might get a weak ultra rare like Tribute/Sunken Warship/Forest Chapel.
Of course, as a business, you can't limit how many packs of cards someone buys with real money. If someone wants to spend $500-$1000 hundreds of packs of cards, they're going to end up with almost every card in the game.
One way some CCG's keep things from getting out of hand is by offering different game options/rulesets. I'm not one of them, but there are A LOT of CCG players out there that love playing with uber decks filled with rares/ultra rares/dieties/etc. If we're talking about rebuilding a game based on hundreds or thousands of players being online at a time, then you can easily offer multiple options for rulesets/game-types. For example...
Beginner Ruleset - 30+ card deck, limit 4 Rares
Limited Ruleset - 30+ card deck, limit 2 Ultra Rares, 6 Rares
Open Ruleset - 30+ card deck, no card limits
Weekly (Rotating) Ruleset - Varying rulesets, eg - "no archers", "no dieties", "Open but no Ultra Rares", or maybe a theme
I think the other thing is that a lot of CCG's are now offering is tournaments. Drafts and Sealed Pack tournaments are extremely popular in most CCG's that I've played and use a population of cards unique to that tournament. Other tournaments can be something like the old themed tournaments SW used to run, or use your own spirits but various different rulesets.
These types of options (rulesets and tournaments) will allow players to play the types of games that they prefer.
We want to encourage players to purchase card packs. The only way people are going to be interested in purchasing card packs is to get the rare and ultra rare spirits.