In CCG games, as the player progresses further and unlocks stronger cards alot of the old cards are ignored and not used anymore. Like for example a CCG with 1000 cards, 100 of them are very strong cards and the others not so much. All players will just use those 100 cards and ignore the rest 900 cards! What can be done in such case to make old cards still usable to players?
One option is to use a crafting system that allows a player to recycle lower tier cards into a higher tier. Depending on the game & your perspective, this may be a potential negative as it creates a way to grind. On the other hand, you could also include special cards that cannot be crafted which allows the designer a bit more control over the experience. I think that Card City Nights had an optional game system that supported crafting, but prevented the player from grinding out cards required to progress the single player story.
A different option is to give some cards powers that require extra cards. Some of the Ascension deckbuilding game sets did this. For instance, some of the Void faction cards from the Storm of Souls set had abilities that could only trigger by removing cards from your deck - typically, you want to hold onto higher power cards, so it was useful to have some low level cards to burn. And in various sets there are cards that trigger from having cards of the same faction in hand, so sometimes it's worth buying more cheap cards from faction X because it increases the chance that when your powerful faction X card is drawn you'll have a matching faction to trigger it.
So the overarching idea is to find ways to turn low level cards into resources of one type or another. Burning them for specials, matching sets in hand for specials, gaining a counter based on the number of type X cards in the discard pile.
Finally, consider alternatives to a linear measure of card strength. For example, having high level cards that only affect other high level cards (perhaps thematically, those low level cards are beneath their notice). By making the card strengths cyclic instead of linear, you support a richer meta game as players try to second guess what their opponent might field. Going back to the example, a player with mostly high power cards that can only hit other higher power cards could easily lose to someone who fielded a lot of low level cards.
From a commercial point of view, a bit of power creep can actually be good. It forces your players to buy the new cards when you release an update in order to stay competitive. But when you exploit this too much, players will notice, call you out on your obvious cash-grabbing and abandon your game. So you need to be careful to not become too greedy here.
Methods you can use to prevent power creep:
- Make sure your game mechanics have the proper tools to allow you to balance cards against each other. In the idealized case, every single card you release and will ever release in the future would be equally good. Not equally good in every possible situation, but all cards should have a justification for existing. In practice this will be impossible to achieve (at least if you want to keep your game interesting), but that shouldn't stop you from trying. One very useful tool for this is having some form of cost mechanic which makes powerful cards harder to play.
- Have new cards which interact with underpowered old cards in interesting ways. Adding a card in a new edition which gives a considerable powerup to some underpowered cards in the previous edition can give them the power boost they need to become competitive again.
- Similarly, get those cards you accidentally made too powerful back in line by adding cards which specifically counter them.
- In a virtual CCG, you always have the last resort option to simply change cards when they turn out to be under- or overpowered. Players tend to hate it when you ruin their decks by nerfing their most powerful cards, but they might forgive you if you don't do it too often and when the end result is a much better game. Making changes to already printed card might be hard in a physical CCG, but it is not unheard of either. Some CCGs publish regular lists of errata which change how some cards work or even outright ban some cards. Casual players likely won't know that these lists even exist and will play with the cards like they are printed, but tournament players will know them.